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 $74.75   11.564%   $83.3941   $83.39   $83.40   $83.40  
  Purchase #2 $117.32   3.369%   $121.2725   $121.27   $121.25   $121.30  
  Purchase #3 $196.66   7.133%   $210.6878   $210.69   $210.70   $210.70  
  Purchase #4 $81.70   8.394%   $88.5579   $88.56   $88.55   $88.60  
  Purchase #5 $124.40   3.869%   $129.213   $129.21   $129.20   $129.20  
  Purchase #6 $53.69   11.248%   $59.7291   $59.73   $59.75   $59.70  
  Purchase #7 $235.88   5.627%   $249.153   $249.15   $249.15   $249.20  
  7 purchase totals = $884.40       $942.0074   $942.00   $942.00   $942.10