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 $214.64   13.688%   $244.0199   $244.02   $244.00   $244.00  
  Purchase #2 $62.96   8.854%   $68.5345   $68.53   $68.55   $68.50  
  Purchase #3 $113.75   5.405%   $119.8982   $119.90   $119.90   $119.90  
  Purchase #4 $87.33   9.757%   $95.8508   $95.85   $95.85   $95.90  
  Purchase #5 $94.72   4.429%   $98.9151   $98.92   $98.90   $98.90  
  Purchase #6 $162.33   13.819%   $184.7624   $184.76   $184.75   $184.80  
  Purchase #7 $129.73   13.538%   $147.2928   $147.29   $147.30   $147.30  
  7 purchase totals = $865.46       $959.2737   $959.27   $959.25   $959.30