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 $114.82   5.708%   $121.3739   $121.37   $121.35   $121.40  
  Purchase #2 $207.68   9.658%   $227.7377   $227.74   $227.75   $227.70  
  Purchase #3 $92.26   6.198%   $97.9783   $97.98   $98.00   $98.00  
  Purchase #4 $158.84   5.208%   $167.1124   $167.11   $167.10   $167.10  
  Purchase #5 $44.79   11.291%   $49.8472   $49.85   $49.85   $49.80  
  Purchase #6 $155.55   3.709%   $161.3193   $161.32   $161.30   $161.30  
  Purchase #7 $32.95   8.343%   $35.699   $35.70   $35.70   $35.70  
  7 purchase totals = $806.89       $861.0678   $861.07   $861.05   $861.00