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 $126.90   12.329%   $142.5455   $142.55   $142.55   $142.50  
  Purchase #2 $240.92   8.429%   $261.2271   $261.23   $261.25   $261.20  
  Purchase #3 $93.49   6.162%   $99.2509   $99.25   $99.25   $99.30  
  Purchase #4 $188.93   11.246%   $210.1771   $210.18   $210.20   $210.20  
  Purchase #5 $26.95   13.638%   $30.6254   $30.63   $30.65   $30.60  
  Purchase #6 $187.84   9.543%   $205.7656   $205.77   $205.75   $205.80  
  Purchase #7 $49.58   6.412%   $52.7591   $52.76   $52.75   $52.80  
  7 purchase totals = $914.61       $1,002.3507   $1,002.37   $1,002.40   $1,002.40