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 $188.64   13.322%   $213.7706   $213.77   $213.75   $213.80  
  Purchase #2 $243.41   10.834%   $269.781   $269.78   $269.80   $269.80  
  Purchase #3 $63.59   11.501%   $70.9035   $70.90   $70.90   $70.90  
  Purchase #4 $193.57   8.161%   $209.3672   $209.37   $209.35   $209.40  
  Purchase #5 $202.31   12.463%   $227.5239   $227.52   $227.50   $227.50  
  Purchase #6 $29.57   11.609%   $33.0028   $33.00   $33.00   $33.00  
  Purchase #7 $226.58   5.758%   $239.6265   $239.63   $239.65   $239.60  
  7 purchase totals = $1,147.67       $1,263.9755   $1,263.97   $1,263.95   $1,264.00