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 $84.48   13.378%   $95.7817   $95.78   $95.80   $95.80  
  Purchase #2 $120.42   4.265%   $125.5559   $125.56   $125.55   $125.60  
  Purchase #3 $232.49   5.608%   $245.528   $245.53   $245.55   $245.50  
  Purchase #4 $116.28   3.134%   $119.9242   $119.92   $119.90   $119.90  
  Purchase #5 $218.94   12.781%   $246.9227   $246.92   $246.90   $246.90  
  Purchase #6 $73.31   3.134%   $75.6075   $75.61   $75.60   $75.60  
  Purchase #7 $30.51   8.515%   $33.1079   $33.11   $33.10   $33.10  
  7 purchase totals = $876.43       $942.4279   $942.43   $942.40   $942.40