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 $57.32   3.244%   $59.1795   $59.18   $59.20   $59.20  
  Purchase #2 $72.56   8.197%   $78.5077   $78.51   $78.50   $78.50  
  Purchase #3 $104.33   9.258%   $113.9889   $113.99   $114.00   $114.00  
  Purchase #4 $182.26   12.676%   $205.3633   $205.36   $205.35   $205.40  
  Purchase #5 $219.87   9.339%   $240.4037   $240.40   $240.40   $240.40  
  Purchase #6 $105.79   13.185%   $119.7384   $119.74   $119.75   $119.70  
  Purchase #7 $202.37   5.776%   $214.0589   $214.06   $214.05   $214.10  
  7 purchase totals = $944.50       $1,031.2404   $1,031.24   $1,031.25   $1,031.30