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 $92.43   6.668%   $98.5932   $98.59   $98.60   $98.60  
  Purchase #2 $17.36   10.577%   $19.1962   $19.20   $19.20   $19.20  
  Purchase #3 $236.67   3.229%   $244.3121   $244.31   $244.30   $244.30  
  Purchase #4 $92.54   7.316%   $99.3102   $99.31   $99.30   $99.30  
  Purchase #5 $62.38   4.588%   $65.242   $65.24   $65.25   $65.20  
  Purchase #6 $77.95   6.485%   $83.0051   $83.01   $83.00   $83.00  
  Purchase #7 $169.68   8.429%   $183.9823   $183.98   $184.00   $184.00  
  7 purchase totals = $749.01       $793.6411   $793.64   $793.65   $793.60