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	$240.81	5.840%	$254.8733	$254.87	$254.85	$254.90
Purchase #2	$111.57	11.434%	$124.3269	$124.33	$124.35	$124.30
Purchase #3	$223.87	9.233%	$244.5399	$244.54	$244.55	$244.50
Purchase #4	$195.25	4.818%	$204.6571	$204.66	$204.65	$204.70
Purchase #5	$98.50	13.454%	$111.7522	$111.75	$111.75	$111.80
Purchase #6	$220.85	9.529%	$241.8948	$241.89	$241.90	$241.90
Purchase #7	$88.31	8.554%	$95.864	$95.86	$95.85	$95.90
7 purchase totals =	$1,179.16		$1,277.9082	$1,277.90	$1,277.90	$1,278.00