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 $183.88   6.719%   $196.2349   $196.23   $196.25   $196.20  
  Purchase #2 $238.73   5.872%   $252.7482   $252.75   $252.75   $252.70  
  Purchase #3 $59.39   7.632%   $63.9226   $63.92   $63.90   $63.90  
  Purchase #4 $242.79   10.155%   $267.4453   $267.45   $267.45   $267.40  
  Purchase #5 $61.67   13.661%   $70.0947   $70.09   $70.10   $70.10  
  Purchase #6 $67.83   11.778%   $75.819   $75.82   $75.80   $75.80  
  Purchase #7 $6.49   8.214%   $7.0231   $7.02   $7.00   $7.00  
  7 purchase totals = $860.78       $933.2878   $933.28   $933.25   $933.10