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	$6.86	13.251%	$7.769	$7.77	$7.75	$7.80
Purchase #2	$113.86	8.251%	$123.2546	$123.25	$123.25	$123.30
Purchase #3	$116.77	7.493%	$125.5196	$125.52	$125.50	$125.50
Purchase #4	$159.90	3.489%	$165.4789	$165.48	$165.50	$165.50
Purchase #5	$131.43	4.462%	$137.2944	$137.29	$137.30	$137.30
Purchase #6	$71.91	8.613%	$78.1036	$78.10	$78.10	$78.10
Purchase #7	$99.48	10.854%	$110.2776	$110.28	$110.30	$110.30
7 purchase totals =	$700.21		$747.6977	$747.69	$747.70	$747.80