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 $92.55   12.136%   $103.7819   $103.78   $103.80   $103.80  
  Purchase #2 $55.95   11.351%   $62.3009   $62.30   $62.30   $62.30  
  Purchase #3 $48.40   8.259%   $52.3974   $52.40   $52.40   $52.40  
  Purchase #4 $239.82   10.161%   $264.1881   $264.19   $264.20   $264.20  
  Purchase #5 $125.80   5.790%   $133.0838   $133.08   $133.10   $133.10  
  Purchase #6 $51.86   12.175%   $58.174   $58.17   $58.15   $58.20  
  Purchase #7 $220.31   13.197%   $249.3843   $249.38   $249.40   $249.40  
  7 purchase totals = $834.69       $923.3104   $923.30   $923.35   $923.40