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 $86.82   9.352%   $94.9394   $94.94   $94.95   $94.90  
  Purchase #2 $180.52   5.553%   $190.5443   $190.54   $190.55   $190.50  
  Purchase #3 $98.71   7.491%   $106.1044   $106.10   $106.10   $106.10  
  Purchase #4 $54.96   7.271%   $58.9561   $58.96   $58.95   $59.00  
  Purchase #5 $176.41   10.352%   $194.672   $194.67   $194.65   $194.70  
  Purchase #6 $25.78   9.183%   $28.1474   $28.15   $28.15   $28.10  
  Purchase #7 $142.80   13.798%   $162.5035   $162.50   $162.50   $162.50  
  7 purchase totals = $766.00       $835.8671   $835.86   $835.85   $835.80