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 $47.65   13.327%   $54.0003   $54.00   $54.00   $54.00  
  Purchase #2 $115.91   8.503%   $125.7658   $125.77   $125.75   $125.80  
  Purchase #3 $66.68   11.864%   $74.5909   $74.59   $74.60   $74.60  
  Purchase #4 $192.71   4.586%   $201.5477   $201.55   $201.55   $201.50  
  Purchase #5 $205.64   8.591%   $223.3065   $223.31   $223.30   $223.30  
  Purchase #6 $156.43   12.848%   $176.5281   $176.53   $176.55   $176.50  
  Purchase #7 $84.58   9.186%   $92.3495   $92.35   $92.35   $92.30  
  7 purchase totals = $869.60       $948.0888   $948.10   $948.10   $948.00