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 $60.35   7.180%   $64.6831   $64.68   $64.70   $64.70  
  Purchase #2 $244.33   10.667%   $270.3927   $270.39   $270.40   $270.40  
  Purchase #3 $217.95   6.377%   $231.8487   $231.85   $231.85   $231.80  
  Purchase #4 $49.62   5.624%   $52.4106   $52.41   $52.40   $52.40  
  Purchase #5 $195.39   7.694%   $210.4233   $210.42   $210.40   $210.40  
  Purchase #6 $221.83   13.620%   $252.0432   $252.04   $252.05   $252.00  
  Purchase #7 $34.47   5.434%   $36.3431   $36.34   $36.35   $36.30  
  7 purchase totals = $1,023.94       $1,118.1447   $1,118.13   $1,118.15   $1,118.00