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 $86.99   12.171%   $97.5776   $97.58   $97.60   $97.60  
  Purchase #2 $44.86   4.110%   $46.7037   $46.70   $46.70   $46.70  
  Purchase #3 $139.36   6.398%   $148.2763   $148.28   $148.30   $148.30  
  Purchase #4 $187.46   5.332%   $197.4554   $197.46   $197.45   $197.50  
  Purchase #5 $80.99   13.624%   $92.0241   $92.02   $92.00   $92.00  
  Purchase #6 $84.44   5.401%   $89.0006   $89.00   $89.00   $89.00  
  Purchase #7 $233.97   12.429%   $263.0501   $263.05   $263.05   $263.10  
  7 purchase totals = $858.07       $934.0878   $934.09   $934.10   $934.20