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 $216.97   5.555%   $229.0227   $229.02   $229.00   $229.00  
  Purchase #2 $185.89   8.264%   $201.2519   $201.25   $201.25   $201.30  
  Purchase #3 $36.62   12.755%   $41.2909   $41.29   $41.30   $41.30  
  Purchase #4 $94.96   13.164%   $107.4605   $107.46   $107.45   $107.50  
  Purchase #5 $75.98   3.531%   $78.6629   $78.66   $78.65   $78.70  
  Purchase #6 $230.95   7.348%   $247.9202   $247.92   $247.90   $247.90  
  Purchase #7 $111.75   6.161%   $118.6349   $118.63   $118.65   $118.60  
  7 purchase totals = $953.12       $1,024.2440   $1,024.23   $1,024.20   $1,024.30