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	$5.51	12.275%	$6.1864	$6.19	$6.20	$6.20
Purchase #2	$35.64	10.485%	$39.3769	$39.38	$39.40	$39.40
Purchase #3	$126.89	3.593%	$131.4492	$131.45	$131.45	$131.40
Purchase #4	$106.85	6.644%	$113.9491	$113.95	$113.95	$113.90
Purchase #5	$57.41	9.233%	$62.7107	$62.71	$62.70	$62.70
Purchase #6	$78.40	13.646%	$89.0985	$89.10	$89.10	$89.10
Purchase #7	$142.72	4.335%	$148.9069	$148.91	$148.90	$148.90
7 purchase totals =	$553.42		$591.6777	$591.69	$591.70	$591.60