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 $56.93   5.287%   $59.9399   $59.94   $59.95   $59.90  
  Purchase #2 $47.25   8.548%   $51.2889   $51.29   $51.30   $51.30  
  Purchase #3 $13.92   13.109%   $15.7448   $15.74   $15.75   $15.70  
  Purchase #4 $215.96   9.172%   $235.7679   $235.77   $235.75   $235.80  
  Purchase #5 $147.59   7.668%   $158.9072   $158.91   $158.90   $158.90  
  Purchase #6 $127.89   4.337%   $133.4366   $133.44   $133.45   $133.40  
  Purchase #7 $79.94   6.277%   $84.9578   $84.96   $84.95   $85.00  
  7 purchase totals = $689.48       $740.0431   $740.05   $740.05   $740.00