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 $126.95   9.598%   $139.1347   $139.13   $139.15   $139.10  
  Purchase #2 $205.98   4.742%   $215.7476   $215.75   $215.75   $215.70  
  Purchase #3 $28.80   7.173%   $30.8658   $30.87   $30.85   $30.90  
  Purchase #4 $241.34   4.385%   $251.9228   $251.92   $251.90   $251.90  
  Purchase #5 $137.37   13.824%   $156.36   $156.36   $156.35   $156.40  
  Purchase #6 $248.33   10.808%   $275.1695   $275.17   $275.15   $275.20  
  Purchase #7 $173.42   5.404%   $182.7916   $182.79   $182.80   $182.80  
  7 purchase totals = $1,162.19       $1,251.9920   $1,251.99   $1,251.95   $1,252.00