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	$129.65	12.846%	$146.3048	$146.30	$146.30	$146.30
Purchase #2	$174.53	12.329%	$196.0478	$196.05	$196.05	$196.00
Purchase #3	$79.28	9.433%	$86.7585	$86.76	$86.75	$86.80
Purchase #4	$9.58	3.296%	$9.8958	$9.90	$9.90	$9.90
Purchase #5	$215.67	11.613%	$240.7158	$240.72	$240.70	$240.70
Purchase #6	$70.44	11.787%	$78.7428	$78.74	$78.75	$78.70
Purchase #7	$210.81	5.381%	$222.1537	$222.15	$222.15	$222.20
7 purchase totals =	$889.96		$980.6192	$980.62	$980.60	$980.60