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 $99.37   11.832%   $111.1275   $111.13   $111.15   $111.10  
  Purchase #2 $97.43   6.668%   $103.9266   $103.93   $103.95   $103.90  
  Purchase #3 $18.25   8.113%   $19.7306   $19.73   $19.75   $19.70  
  Purchase #4 $182.98   7.183%   $196.1235   $196.12   $196.10   $196.10  
  Purchase #5 $95.82   5.865%   $101.4398   $101.44   $101.45   $101.40  
  Purchase #6 $68.97   9.269%   $75.3628   $75.36   $75.35   $75.40  
  Purchase #7 $140.48   9.224%   $153.4379   $153.44   $153.45   $153.40  
  7 purchase totals = $703.30       $761.1487   $761.15   $761.20   $761.00