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 $93.70   4.756%   $98.1564   $98.16   $98.15   $98.20  
  Purchase #2 $115.27   3.547%   $119.3586   $119.36   $119.35   $119.40  
  Purchase #3 $88.88   7.137%   $95.2234   $95.22   $95.20   $95.20  
  Purchase #4 $114.72   9.856%   $126.0268   $126.03   $126.05   $126.00  
  Purchase #5 $235.36   7.784%   $253.6804   $253.68   $253.70   $253.70  
  Purchase #6 $125.92   6.683%   $134.3352   $134.34   $134.35   $134.30  
  Purchase #7 $150.49   12.775%   $169.7151   $169.72   $169.70   $169.70  
  7 purchase totals = $924.34       $996.4959   $996.51   $996.50   $996.50