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 $84.89   4.773%   $88.9418   $88.94   $88.95   $88.90  
  Purchase #2 $14.32   7.594%   $15.4075   $15.41   $15.40   $15.40  
  Purchase #3 $191.90   3.298%   $198.2289   $198.23   $198.25   $198.20  
  Purchase #4 $56.53   8.390%   $61.2729   $61.27   $61.25   $61.30  
  Purchase #5 $88.53   9.626%   $97.0519   $97.05   $97.05   $97.10  
  Purchase #6 $69.95   4.852%   $73.344   $73.34   $73.35   $73.30  
  Purchase #7 $207.31   9.583%   $227.1765   $227.18   $227.20   $227.20  
  7 purchase totals = $713.43       $761.4235   $761.42   $761.45   $761.40