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 $214.65   4.649%   $224.6291   $224.63   $224.65   $224.60  
  Purchase #2 $87.42   10.272%   $96.3998   $96.40   $96.40   $96.40  
  Purchase #3 $64.49   8.534%   $69.9936   $69.99   $70.00   $70.00  
  Purchase #4 $197.48   8.757%   $214.7733   $214.77   $214.75   $214.80  
  Purchase #5 $93.95   7.539%   $101.0329   $101.03   $101.05   $101.00  
  Purchase #6 $236.92   3.816%   $245.9609   $245.96   $245.95   $246.00  
  Purchase #7 $38.73   7.138%   $41.4945   $41.49   $41.50   $41.50  
  7 purchase totals = $933.64       $994.2841   $994.27   $994.30   $994.30