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 $249.74   9.434%   $273.3005   $273.30   $273.30   $273.30  
  Purchase #2 $231.38   6.218%   $245.7672   $245.77   $245.75   $245.80  
  Purchase #3 $119.39   4.287%   $124.5082   $124.51   $124.50   $124.50  
  Purchase #4 $64.73   9.255%   $70.7208   $70.72   $70.70   $70.70  
  Purchase #5 $17.35   6.815%   $18.5324   $18.53   $18.55   $18.50  
  Purchase #6 $149.95   11.300%   $166.8944   $166.89   $166.90   $166.90  
  Purchase #7 $50.43   4.553%   $52.7261   $52.73   $52.75   $52.70  
  7 purchase totals = $882.97       $952.4496   $952.45   $952.45   $952.40