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 $65.41   11.709%   $73.0689   $73.07   $73.05   $73.10  
  Purchase #2 $250.83   9.652%   $275.0401   $275.04   $275.05   $275.00  
  Purchase #3 $58.49   8.313%   $63.3523   $63.35   $63.35   $63.40  
  Purchase #4 $194.64   13.770%   $221.4419   $221.44   $221.45   $221.40  
  Purchase #5 $40.99   9.758%   $44.9898   $44.99   $45.00   $45.00  
  Purchase #6 $146.92   9.401%   $160.7319   $160.73   $160.75   $160.70  
  Purchase #7 $116.97   3.457%   $121.0137   $121.01   $121.00   $121.00  
  7 purchase totals = $874.25       $959.6386   $959.63   $959.65   $959.60