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 $244.97   9.733%   $268.8129   $268.81   $268.80   $268.80  
  Purchase #2 $79.30   11.737%   $88.6074   $88.61   $88.60   $88.60  
  Purchase #3 $194.94   11.386%   $217.1359   $217.14   $217.15   $217.10  
  Purchase #4 $244.69   7.751%   $263.6559   $263.66   $263.65   $263.70  
  Purchase #5 $35.84   5.738%   $37.8965   $37.90   $37.90   $37.90  
  Purchase #6 $129.55   7.141%   $138.8012   $138.80   $138.80   $138.80  
  Purchase #7 $67.63   12.809%   $76.2927   $76.29   $76.30   $76.30  
  7 purchase totals = $996.92       $1,091.2025   $1,091.21   $1,091.20   $1,091.20