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 $35.94   7.706%   $38.7095   $38.71   $38.70   $38.70  
  Purchase #2 $159.36   3.282%   $164.5902   $164.59   $164.60   $164.60  
  Purchase #3 $13.78   5.204%   $14.4971   $14.50   $14.50   $14.50  
  Purchase #4 $245.82   8.701%   $267.2088   $267.21   $267.20   $267.20  
  Purchase #5 $34.70   5.513%   $36.613   $36.61   $36.60   $36.60  
  Purchase #6 $105.73   4.519%   $110.5079   $110.51   $110.50   $110.50  
  Purchase #7 $92.71   3.726%   $96.1644   $96.16   $96.15   $96.20  
  7 purchase totals = $688.04       $728.2909   $728.29   $728.25   $728.30