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 $83.89   9.274%   $91.67   $91.67   $91.65   $91.70  
  Purchase #2 $37.87   10.696%   $41.9206   $41.92   $41.90   $41.90  
  Purchase #3 $95.50   9.628%   $104.6947   $104.69   $104.70   $104.70  
  Purchase #4 $59.34   7.330%   $63.6896   $63.69   $63.70   $63.70  
  Purchase #5 $219.92   13.498%   $249.6048   $249.60   $249.60   $249.60  
  Purchase #6 $170.81   9.311%   $186.7141   $186.71   $186.70   $186.70  
  Purchase #7 $202.67   10.776%   $224.5097   $224.51   $224.50   $224.50  
  7 purchase totals = $870.00       $962.8035   $962.79   $962.75   $962.80