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 $138.85   9.157%   $151.5645   $151.56   $151.55   $151.60  
  Purchase #2 $76.84   6.716%   $82.0006   $82.00   $82.00   $82.00  
  Purchase #3 $59.51   7.543%   $63.9988   $64.00   $64.00   $64.00  
  Purchase #4 $238.93   9.771%   $262.2759   $262.28   $262.30   $262.30  
  Purchase #5 $205.34   4.833%   $215.2641   $215.26   $215.25   $215.30  
  Purchase #6 $53.83   13.106%   $60.885   $60.89   $60.90   $60.90  
  Purchase #7 $18.79   3.791%   $19.5023   $19.50   $19.50   $19.50  
  7 purchase totals = $792.09       $855.4912   $855.49   $855.50   $855.60