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 $208.36   13.279%   $236.0281   $236.03   $236.05   $236.00  
  Purchase #2 $97.91   12.108%   $109.7649   $109.76   $109.75   $109.80  
  Purchase #3 $212.62   8.646%   $231.0031   $231.00   $231.00   $231.00  
  Purchase #4 $86.37   8.244%   $93.4903   $93.49   $93.50   $93.50  
  Purchase #5 $72.41   5.201%   $76.176   $76.18   $76.20   $76.20  
  Purchase #6 $238.26   13.604%   $270.6729   $270.67   $270.65   $270.70  
  Purchase #7 $38.42   5.223%   $40.4267   $40.43   $40.45   $40.40  
  7 purchase totals = $954.35       $1,057.5620   $1,057.56   $1,057.60   $1,057.60