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 $57.83   13.710%   $65.7585   $65.76   $65.75   $65.80  
  Purchase #2 $40.70   7.836%   $43.8893   $43.89   $43.90   $43.90  
  Purchase #3 $229.62   8.673%   $249.5349   $249.53   $249.55   $249.50  
  Purchase #4 $95.35   12.353%   $107.1286   $107.13   $107.15   $107.10  
  Purchase #5 $216.94   9.250%   $237.007   $237.01   $237.00   $237.00  
  Purchase #6 $21.32   9.154%   $23.2716   $23.27   $23.25   $23.30  
  Purchase #7 $198.74   9.250%   $217.1235   $217.12   $217.10   $217.10  
  7 purchase totals = $860.50       $943.7134   $943.71   $943.70   $943.70