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 $93.37   9.606%   $102.3391   $102.34   $102.35   $102.30  
  Purchase #2 $243.76   10.434%   $269.1939   $269.19   $269.20   $269.20  
  Purchase #3 $83.43   4.305%   $87.0217   $87.02   $87.00   $87.00  
  Purchase #4 $99.60   13.684%   $113.2293   $113.23   $113.25   $113.20  
  Purchase #5 $223.97   5.419%   $236.1069   $236.11   $236.10   $236.10  
  Purchase #6 $21.46   6.286%   $22.809   $22.81   $22.80   $22.80  
  Purchase #7 $146.46   10.312%   $161.563   $161.56   $161.55   $161.60  
  7 purchase totals = $912.05       $992.2629   $992.26   $992.25   $992.20