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	$250.73	4.304%	$261.5214	$261.52	$261.50	$261.50
Purchase #2	$35.96	4.500%	$37.5782	$37.58	$37.60	$37.60
Purchase #3	$156.44	9.129%	$170.7214	$170.72	$170.70	$170.70
Purchase #4	$221.68	3.461%	$229.3523	$229.35	$229.35	$229.40
Purchase #5	$138.53	12.171%	$155.3905	$155.39	$155.40	$155.40
Purchase #6	$50.74	9.423%	$55.5212	$55.52	$55.50	$55.50
Purchase #7	$127.64	13.154%	$144.4298	$144.43	$144.45	$144.40
7 purchase totals =	$981.72		$1,054.5148	$1,054.51	$1,054.50	$1,054.50