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 $226.65   10.544%   $250.548   $250.55   $250.55   $250.50  
  Purchase #2 $106.92   9.106%   $116.6561   $116.66   $116.65   $116.70  
  Purchase #3 $24.37   3.627%   $25.2539   $25.25   $25.25   $25.30  
  Purchase #4 $31.75   5.801%   $33.5918   $33.59   $33.60   $33.60  
  Purchase #5 $197.36   12.551%   $222.1307   $222.13   $222.15   $222.10  
  Purchase #6 $60.68   13.703%   $68.995   $69.00   $69.00   $69.00  
  Purchase #7 $225.71   10.528%   $249.4727   $249.47   $249.45   $249.50  
  7 purchase totals = $873.44       $966.6482   $966.65   $966.65   $966.70