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 $229.48   10.355%   $253.2427   $253.24   $253.25   $253.20  
  Purchase #2 $59.95   3.836%   $62.2497   $62.25   $62.25   $62.20  
  Purchase #3 $60.44   10.566%   $66.8261   $66.83   $66.85   $66.80  
  Purchase #4 $242.90   10.872%   $269.3081   $269.31   $269.30   $269.30  
  Purchase #5 $44.42   3.617%   $46.0267   $46.03   $46.05   $46.00  
  Purchase #6 $172.84   12.677%   $194.7509   $194.75   $194.75   $194.80  
  Purchase #7 $69.37   7.243%   $74.3945   $74.39   $74.40   $74.40  
  7 purchase totals = $879.40       $966.7987   $966.80   $966.85   $966.70