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	$55.32	11.759%	$61.8251	$61.83	$61.85	$61.80
Purchase #2	$203.30	3.239%	$209.8849	$209.88	$209.90	$209.90
Purchase #3	$87.78	12.661%	$98.8938	$98.89	$98.90	$98.90
Purchase #4	$124.39	8.267%	$134.6733	$134.67	$134.65	$134.70
Purchase #5	$111.64	3.649%	$115.7137	$115.71	$115.70	$115.70
Purchase #6	$20.73	5.658%	$21.9029	$21.90	$21.90	$21.90
Purchase #7	$21.43	7.209%	$22.9749	$22.97	$22.95	$23.00
7 purchase totals =	$624.59		$665.8686	$665.85	$665.85	$665.90