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 $23.91   8.119%   $25.8513   $25.85   $25.85   $25.90  
  Purchase #2 $246.93   6.106%   $262.0075   $262.01   $262.00   $262.00  
  Purchase #3 $11.82   11.828%   $13.2181   $13.22   $13.20   $13.20  
  Purchase #4 $138.27   8.170%   $149.5667   $149.57   $149.55   $149.60  
  Purchase #5 $84.44   13.342%   $95.706   $95.71   $95.70   $95.70  
  Purchase #6 $63.76   4.428%   $66.5833   $66.58   $66.60   $66.60  
  Purchase #7 $169.82   3.290%   $175.4071   $175.41   $175.40   $175.40  
  7 purchase totals = $738.95       $788.3400   $788.35   $788.30   $788.40