Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.82   11.397%   $193.6303   $193.63   $193.65   $193.60  
  Purchase #2 $247.57   10.489%   $273.5376   $273.54   $273.55   $273.50  
  Purchase #3 $109.46   13.724%   $124.4823   $124.48   $124.50   $124.50  
  Purchase #4 $140.52   8.701%   $152.7466   $152.75   $152.75   $152.70  
  Purchase #5 $239.94   13.373%   $272.0272   $272.03   $272.05   $272.00  
  Purchase #6 $236.83   8.298%   $256.4822   $256.48   $256.50   $256.50  
  Purchase #7 $146.67   11.377%   $163.3566   $163.36   $163.35   $163.40  
  7 purchase totals = $1,294.81       $1,436.2628   $1,436.27   $1,436.35   $1,436.20