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 $215.33   12.369%   $241.9642   $241.96   $241.95   $242.00  
  Purchase #2 $87.78   11.361%   $97.7527   $97.75   $97.75   $97.80  
  Purchase #3 $215.75   7.490%   $231.9097   $231.91   $231.90   $231.90  
  Purchase #4 $218.67   10.307%   $241.2083   $241.21   $241.20   $241.20  
  Purchase #5 $187.43   5.664%   $198.046   $198.05   $198.05   $198.00  
  Purchase #6 $12.78   13.545%   $14.5111   $14.51   $14.50   $14.50  
  Purchase #7 $57.35   4.706%   $60.0489   $60.05   $60.05   $60.00  
  7 purchase totals = $995.09       $1,085.4409   $1,085.44   $1,085.40   $1,085.40