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 $29.89   9.613%   $32.7633   $32.76   $32.75   $32.80  
  Purchase #2 $246.36   4.241%   $256.8081   $256.81   $256.80   $256.80  
  Purchase #3 $65.51   11.573%   $73.0915   $73.09   $73.10   $73.10  
  Purchase #4 $123.71   12.567%   $139.2566   $139.26   $139.25   $139.30  
  Purchase #5 $57.45   10.508%   $63.4868   $63.49   $63.50   $63.50  
  Purchase #6 $16.32   11.282%   $18.1612   $18.16   $18.15   $18.20  
  Purchase #7 $112.75   4.419%   $117.7324   $117.73   $117.75   $117.70  
  7 purchase totals = $651.99       $701.2999   $701.30   $701.30   $701.40