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 $65.26   10.108%   $71.8565   $71.86   $71.85   $71.90  
  Purchase #2 $195.95   4.498%   $204.7638   $204.76   $204.75   $204.80  
  Purchase #3 $87.68   5.476%   $92.4814   $92.48   $92.50   $92.50  
  Purchase #4 $121.46   7.334%   $130.3679   $130.37   $130.35   $130.40  
  Purchase #5 $227.88   13.832%   $259.4004   $259.40   $259.40   $259.40  
  Purchase #6 $82.60   8.197%   $89.3707   $89.37   $89.35   $89.40  
  Purchase #7 $110.48   4.592%   $115.5532   $115.55   $115.55   $115.60  
  7 purchase totals = $891.31       $963.7939   $963.79   $963.75   $964.00