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 $66.29   12.567%   $74.6207   $74.62   $74.60   $74.60  
  Purchase #2 $169.25   10.248%   $186.5947   $186.59   $186.60   $186.60  
  Purchase #3 $208.66   10.717%   $231.0221   $231.02   $231.00   $231.00  
  Purchase #4 $83.81   13.156%   $94.836   $94.84   $94.85   $94.80  
  Purchase #5 $132.71   7.865%   $143.1476   $143.15   $143.15   $143.10  
  Purchase #6 $152.92   10.745%   $169.3513   $169.35   $169.35   $169.40  
  Purchase #7 $56.63   11.116%   $62.925   $62.93   $62.95   $62.90  
  7 purchase totals = $870.27       $962.4974   $962.50   $962.50   $962.40