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 $70.28   7.832%   $75.7843   $75.78   $75.80   $75.80  
  Purchase #2 $188.68   4.757%   $197.6555   $197.66   $197.65   $197.70  
  Purchase #3 $65.76   5.208%   $69.1848   $69.18   $69.20   $69.20  
  Purchase #4 $244.53   8.230%   $264.6548   $264.65   $264.65   $264.70  
  Purchase #5 $16.96   5.602%   $17.9101   $17.91   $17.90   $17.90  
  Purchase #6 $165.99   11.291%   $184.7319   $184.73   $184.75   $184.70  
  Purchase #7 $27.76   5.111%   $29.1788   $29.18   $29.20   $29.20  
  7 purchase totals = $779.96       $839.1002   $839.09   $839.15   $839.20