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 $83.78   12.119%   $93.9333   $93.93   $93.95   $93.90  
  Purchase #2 $207.83   13.532%   $235.9536   $235.95   $235.95   $236.00  
  Purchase #3 $24.33   6.439%   $25.8966   $25.90   $25.90   $25.90  
  Purchase #4 $250.39   8.349%   $271.2951   $271.30   $271.30   $271.30  
  Purchase #5 $163.49   4.148%   $170.2716   $170.27   $170.25   $170.30  
  Purchase #6 $47.62   11.557%   $53.1234   $53.12   $53.10   $53.10  
  Purchase #7 $177.63   5.565%   $187.5151   $187.52   $187.50   $187.50  
  7 purchase totals = $955.07       $1,037.9887   $1,037.99   $1,037.95   $1,038.00