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 $57.45   10.554%   $63.5133   $63.51   $63.50   $63.50  
  Purchase #2 $173.29   12.325%   $194.648   $194.65   $194.65   $194.60  
  Purchase #3 $169.86   5.725%   $179.5845   $179.58   $179.60   $179.60  
  Purchase #4 $160.67   12.865%   $181.3402   $181.34   $181.35   $181.30  
  Purchase #5 $93.65   5.633%   $98.9253   $98.93   $98.95   $98.90  
  Purchase #6 $35.63   6.651%   $37.9998   $38.00   $38.00   $38.00  
  Purchase #7 $57.56   8.379%   $62.383   $62.38   $62.40   $62.40  
  7 purchase totals = $748.11       $818.3941   $818.39   $818.45   $818.30