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 $214.60   13.718%   $244.0388   $244.04   $244.05   $244.00  
  Purchase #2 $34.89   5.419%   $36.7807   $36.78   $36.80   $36.80  
  Purchase #3 $37.90   3.551%   $39.2458   $39.25   $39.25   $39.20  
  Purchase #4 $123.86   7.120%   $132.6788   $132.68   $132.70   $132.70  
  Purchase #5 $86.42   3.607%   $89.5372   $89.54   $89.55   $89.50  
  Purchase #6 $82.67   13.645%   $93.9503   $93.95   $93.95   $94.00  
  Purchase #7 $163.94   8.806%   $178.3766   $178.38   $178.40   $178.40  
  7 purchase totals = $744.28       $814.6082   $814.62   $814.70   $814.60