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 $210.34   13.376%   $238.4751   $238.48   $238.50   $238.50  
  Purchase #2 $146.55   3.808%   $152.1306   $152.13   $152.15   $152.10  
  Purchase #3 $60.53   10.630%   $66.9643   $66.96   $66.95   $67.00  
  Purchase #4 $127.29   11.199%   $141.5452   $141.55   $141.55   $141.50  
  Purchase #5 $183.59   12.733%   $206.9665   $206.97   $206.95   $207.00  
  Purchase #6 $249.98   9.330%   $273.3031   $273.30   $273.30   $273.30  
  Purchase #7 $150.97   9.496%   $165.3061   $165.31   $165.30   $165.30  
  7 purchase totals = $1,129.25       $1,244.6909   $1,244.70   $1,244.70   $1,244.70