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 $59.91   3.225%   $61.8421   $61.84   $61.85   $61.80  
  Purchase #2 $115.32   11.198%   $128.2335   $128.23   $128.25   $128.20  
  Purchase #3 $104.47   9.446%   $114.3382   $114.34   $114.35   $114.30  
  Purchase #4 $193.57   4.383%   $202.0542   $202.05   $202.05   $202.10  
  Purchase #5 $16.58   5.412%   $17.4773   $17.48   $17.50   $17.50  
  Purchase #6 $111.60   5.186%   $117.3876   $117.39   $117.40   $117.40  
  Purchase #7 $120.68   8.471%   $130.9028   $130.90   $130.90   $130.90  
  7 purchase totals = $722.13       $772.2357   $772.23   $772.30   $772.20