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 $165.95   5.631%   $175.2946   $175.29   $175.30   $175.30  
  Purchase #2 $28.27   9.152%   $30.8573   $30.86   $30.85   $30.90  
  Purchase #3 $206.99   10.714%   $229.1669   $229.17   $229.15   $229.20  
  Purchase #4 $183.81   9.761%   $201.7517   $201.75   $201.75   $201.80  
  Purchase #5 $177.67   13.352%   $201.3925   $201.39   $201.40   $201.40  
  Purchase #6 $107.76   4.852%   $112.9885   $112.99   $113.00   $113.00  
  Purchase #7 $65.77   10.826%   $72.8903   $72.89   $72.90   $72.90  
  7 purchase totals = $936.22       $1,024.3418   $1,024.34   $1,024.35   $1,024.50