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	$245.78	13.125%	$278.0386	$278.04	$278.05	$278.00
Purchase #2	$119.38	11.734%	$133.388	$133.39	$133.40	$133.40
Purchase #3	$88.33	10.234%	$97.3697	$97.37	$97.35	$97.40
Purchase #4	$126.38	11.323%	$140.69	$140.69	$140.70	$140.70
Purchase #5	$35.60	4.736%	$37.286	$37.29	$37.30	$37.30
Purchase #6	$146.46	6.431%	$155.8788	$155.88	$155.90	$155.90
Purchase #7	$68.29	5.240%	$71.8684	$71.87	$71.85	$71.90
7 purchase totals =	$830.22		$914.5195	$914.53	$914.55	$914.60