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 $220.27   9.534%   $241.2705   $241.27   $241.25   $241.30  
  Purchase #2 $83.63   4.334%   $87.2545   $87.25   $87.25   $87.30  
  Purchase #3 $16.63   5.407%   $17.5292   $17.53   $17.55   $17.50  
  Purchase #4 $21.43   10.340%   $23.6459   $23.65   $23.65   $23.60  
  Purchase #5 $58.59   3.647%   $60.7268   $60.73   $60.75   $60.70  
  Purchase #6 $221.99   10.786%   $245.9338   $245.93   $245.95   $245.90  
  Purchase #7 $143.92   3.862%   $149.4782   $149.48   $149.50   $149.50  
  7 purchase totals = $766.46       $825.8389   $825.84   $825.90   $825.80