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 $105.55   12.753%   $119.0108   $119.01   $119.00   $119.00  
  Purchase #2 $146.54   3.118%   $151.1091   $151.11   $151.10   $151.10  
  Purchase #3 $42.98   7.304%   $46.1193   $46.12   $46.10   $46.10  
  Purchase #4 $98.91   11.673%   $110.4558   $110.46   $110.45   $110.50  
  Purchase #5 $154.28   8.288%   $167.0667   $167.07   $167.05   $167.10  
  Purchase #6 $223.34   11.555%   $249.1469   $249.15   $249.15   $249.10  
  Purchase #7 $122.47   13.577%   $139.0978   $139.10   $139.10   $139.10  
  7 purchase totals = $894.07       $982.0064   $982.02   $981.95   $982.00