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 $68.94   3.637%   $71.4473   $71.45   $71.45   $71.40  
  Purchase #2 $236.83   12.551%   $266.5545   $266.55   $266.55   $266.60  
  Purchase #3 $143.27   7.566%   $154.1098   $154.11   $154.10   $154.10  
  Purchase #4 $50.33   10.290%   $55.509   $55.51   $55.50   $55.50  
  Purchase #5 $68.97   3.221%   $71.1915   $71.19   $71.20   $71.20  
  Purchase #6 $144.81   10.278%   $159.6936   $159.69   $159.70   $159.70  
  Purchase #7 $109.85   5.859%   $116.2861   $116.29   $116.30   $116.30  
  7 purchase totals = $823.00       $894.7918   $894.79   $894.80   $894.80