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 $242.87   13.449%   $275.5336   $275.53   $275.55   $275.50  
  Purchase #2 $52.39   5.399%   $55.2185   $55.22   $55.20   $55.20  
  Purchase #3 $199.89   4.374%   $208.6332   $208.63   $208.65   $208.60  
  Purchase #4 $158.35   3.748%   $164.285   $164.29   $164.30   $164.30  
  Purchase #5 $26.62   13.835%   $30.3029   $30.30   $30.30   $30.30  
  Purchase #6 $229.68   3.712%   $238.2057   $238.21   $238.20   $238.20  
  Purchase #7 $48.35   9.278%   $52.8359   $52.84   $52.85   $52.80  
  7 purchase totals = $958.15       $1,025.0148   $1,025.02   $1,025.05   $1,024.90