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 $14.67   3.582%   $15.1955   $15.20   $15.20   $15.20  
  Purchase #2 $187.72   8.310%   $203.3195   $203.32   $203.30   $203.30  
  Purchase #3 $92.88   5.109%   $97.6252   $97.63   $97.65   $97.60  
  Purchase #4 $70.25   6.280%   $74.6617   $74.66   $74.65   $74.70  
  Purchase #5 $134.71   12.783%   $151.93   $151.93   $151.95   $151.90  
  Purchase #6 $212.34   5.863%   $224.7895   $224.79   $224.80   $224.80  
  Purchase #7 $242.26   7.652%   $260.7977   $260.80   $260.80   $260.80  
  7 purchase totals = $954.83       $1,028.3191   $1,028.33   $1,028.35   $1,028.30