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 $171.45   13.571%   $194.7175   $194.72   $194.70   $194.70  
  Purchase #2 $223.92   7.659%   $241.07   $241.07   $241.05   $241.10  
  Purchase #3 $69.77   10.562%   $77.1391   $77.14   $77.15   $77.10  
  Purchase #4 $54.92   10.822%   $60.8634   $60.86   $60.85   $60.90  
  Purchase #5 $237.84   6.601%   $253.5398   $253.54   $253.55   $253.50  
  Purchase #6 $92.86   9.369%   $101.5601   $101.56   $101.55   $101.60  
  Purchase #7 $28.51   8.504%   $30.9345   $30.93   $30.95   $30.90  
  7 purchase totals = $879.27       $959.8244   $959.82   $959.80   $959.80