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	$89.76	11.469%	$100.0546	$100.05	$100.05	$100.10
Purchase #2	$182.49	7.758%	$196.6476	$196.65	$196.65	$196.60
Purchase #3	$111.99	13.171%	$126.7402	$126.74	$126.75	$126.70
Purchase #4	$23.75	9.234%	$25.9431	$25.94	$25.95	$25.90
Purchase #5	$98.94	9.415%	$108.2552	$108.26	$108.25	$108.30
Purchase #6	$90.72	3.818%	$94.1837	$94.18	$94.20	$94.20
Purchase #7	$172.53	11.784%	$192.8609	$192.86	$192.85	$192.90
7 purchase totals =	$770.18		$844.6853	$844.68	$844.70	$844.70