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 $146.73   5.137%   $154.2675   $154.27   $154.25   $154.30  
  Purchase #2 $47.31   4.306%   $49.3472   $49.35   $49.35   $49.30  
  Purchase #3 $63.43   12.779%   $71.5357   $71.54   $71.55   $71.50  
  Purchase #4 $98.66   9.315%   $107.8502   $107.85   $107.85   $107.90  
  Purchase #5 $207.67   8.845%   $226.0384   $226.04   $226.05   $226.00  
  Purchase #6 $5.62   4.335%   $5.8636   $5.86   $5.85   $5.90  
  Purchase #7 $91.83   7.137%   $98.3839   $98.38   $98.40   $98.40  
  7 purchase totals = $661.25       $713.2865   $713.29   $713.30   $713.30