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 $84.87   8.652%   $92.213   $92.21   $92.20   $92.20  
  Purchase #2 $207.33   9.129%   $226.2572   $226.26   $226.25   $226.30  
  Purchase #3 $235.82   3.445%   $243.944   $243.94   $243.95   $243.90  
  Purchase #4 $115.61   8.164%   $125.0484   $125.05   $125.05   $125.00  
  Purchase #5 $41.49   8.701%   $45.1   $45.10   $45.10   $45.10  
  Purchase #6 $62.47   13.739%   $71.0528   $71.05   $71.05   $71.10  
  Purchase #7 $27.73   5.166%   $29.1625   $29.16   $29.15   $29.20  
  7 purchase totals = $775.32       $832.7779   $832.77   $832.75   $832.80