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 $63.66   7.512%   $68.4421   $68.44   $68.45   $68.40  
  Purchase #2 $106.51   10.335%   $117.5178   $117.52   $117.50   $117.50  
  Purchase #3 $83.35   13.389%   $94.5097   $94.51   $94.50   $94.50  
  Purchase #4 $101.54   5.299%   $106.9206   $106.92   $106.90   $106.90  
  Purchase #5 $216.73   9.213%   $236.6973   $236.70   $236.70   $236.70  
  Purchase #6 $104.56   4.538%   $109.3049   $109.30   $109.30   $109.30  
  Purchase #7 $39.45   7.313%   $42.335   $42.34   $42.35   $42.30  
  7 purchase totals = $715.80       $775.7274   $775.73   $775.70   $775.60