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	$129.90	8.655%	$141.1428	$141.14	$141.15	$141.10
Purchase #2	$145.25	9.188%	$158.5956	$158.60	$158.60	$158.60
Purchase #3	$172.31	4.186%	$179.5229	$179.52	$179.50	$179.50
Purchase #4	$225.69	8.745%	$245.4266	$245.43	$245.45	$245.40
Purchase #5	$220.41	10.677%	$243.9432	$243.94	$243.95	$243.90
Purchase #6	$77.93	13.313%	$88.3048	$88.30	$88.30	$88.30
Purchase #7	$40.60	7.714%	$43.7319	$43.73	$43.75	$43.70
7 purchase totals =	$1,012.09		$1,100.6678	$1,100.66	$1,100.70	$1,100.50