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	$81.63	8.417%	$88.5008	$88.50	$88.50	$88.50
Purchase #2	$172.93	10.615%	$191.2865	$191.29	$191.30	$191.30
Purchase #3	$248.61	4.120%	$258.8527	$258.85	$258.85	$258.90
Purchase #4	$95.41	4.195%	$99.4124	$99.41	$99.40	$99.40
Purchase #5	$96.53	4.245%	$100.6277	$100.63	$100.65	$100.60
Purchase #6	$159.73	6.675%	$170.392	$170.39	$170.40	$170.40
Purchase #7	$111.32	13.342%	$126.1723	$126.17	$126.15	$126.20
7 purchase totals =	$966.16		$1,035.2444	$1,035.24	$1,035.25	$1,035.30