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	$86.28	7.197%	$92.4896	$92.49	$92.50	$92.50
Purchase #2	$59.73	13.384%	$67.7243	$67.72	$67.70	$67.70
Purchase #3	$174.91	4.485%	$182.7547	$182.75	$182.75	$182.80
Purchase #4	$159.90	11.862%	$178.8673	$178.87	$178.85	$178.90
Purchase #5	$9.53	13.279%	$10.7955	$10.80	$10.80	$10.80
Purchase #6	$144.77	5.812%	$153.184	$153.18	$153.20	$153.20
Purchase #7	$71.58	12.486%	$80.5175	$80.52	$80.50	$80.50
7 purchase totals =	$706.70		$766.3329	$766.33	$766.30	$766.40