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 $177.38   11.761%   $198.2417   $198.24   $198.25   $198.20  
  Purchase #2 $14.63   9.139%   $15.967   $15.97   $15.95   $16.00  
  Purchase #3 $127.55   6.827%   $136.2578   $136.26   $136.25   $136.30  
  Purchase #4 $62.82   9.312%   $68.6698   $68.67   $68.65   $68.70  
  Purchase #5 $56.53   9.170%   $61.7138   $61.71   $61.70   $61.70  
  Purchase #6 $222.66   6.799%   $237.7987   $237.80   $237.80   $237.80  
  Purchase #7 $201.76   10.169%   $222.277   $222.28   $222.30   $222.30  
  7 purchase totals = $863.33       $940.9258   $940.93   $940.90   $941.00