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 $62.66   4.538%   $65.5035   $65.50   $65.50   $65.50  
  Purchase #2 $40.85   10.560%   $45.1638   $45.16   $45.15   $45.20  
  Purchase #3 $111.48   9.338%   $121.89   $121.89   $121.90   $121.90  
  Purchase #4 $207.55   3.746%   $215.3248   $215.32   $215.30   $215.30  
  Purchase #5 $184.53   11.584%   $205.906   $205.91   $205.90   $205.90  
  Purchase #6 $209.70   12.170%   $235.2205   $235.22   $235.20   $235.20  
  Purchase #7 $44.80   5.576%   $47.298   $47.30   $47.30   $47.30  
  7 purchase totals = $861.57       $936.3066   $936.30   $936.25   $936.30