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 $222.86   8.129%   $240.9763   $240.98   $241.00   $241.00  
  Purchase #2 $215.99   13.779%   $245.7513   $245.75   $245.75   $245.80  
  Purchase #3 $166.74   6.361%   $177.3463   $177.35   $177.35   $177.30  
  Purchase #4 $58.55   10.598%   $64.7551   $64.76   $64.75   $64.80  
  Purchase #5 $115.61   6.342%   $122.942   $122.94   $122.95   $122.90  
  Purchase #6 $238.36   9.269%   $260.4536   $260.45   $260.45   $260.50  
  Purchase #7 $134.26   5.433%   $141.5543   $141.55   $141.55   $141.60  
  7 purchase totals = $1,152.37       $1,253.7789   $1,253.78   $1,253.80   $1,253.90