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 $81.93   6.359%   $87.1399   $87.14   $87.15   $87.10  
  Purchase #2 $116.87   7.748%   $125.9251   $125.93   $125.95   $125.90  
  Purchase #3 $159.76   6.694%   $170.4543   $170.45   $170.45   $170.50  
  Purchase #4 $240.34   10.458%   $265.4748   $265.47   $265.45   $265.50  
  Purchase #5 $233.62   8.319%   $253.0548   $253.05   $253.05   $253.10  
  Purchase #6 $60.37   13.339%   $68.4228   $68.42   $68.40   $68.40  
  Purchase #7 $60.76   5.566%   $64.1419   $64.14   $64.15   $64.10  
  7 purchase totals = $953.65       $1,034.6136   $1,034.60   $1,034.60   $1,034.60