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	$151.87	8.796%	$165.2285	$165.23	$165.25	$165.20
Purchase #2	$7.32	11.553%	$8.1657	$8.17	$8.15	$8.20
Purchase #3	$92.79	8.437%	$100.6187	$100.62	$100.60	$100.60
Purchase #4	$166.32	3.520%	$172.1745	$172.17	$172.15	$172.20
Purchase #5	$37.69	5.151%	$39.6314	$39.63	$39.65	$39.60
Purchase #6	$161.46	13.393%	$183.0843	$183.08	$183.10	$183.10
Purchase #7	$24.89	13.579%	$28.2698	$28.27	$28.25	$28.30
7 purchase totals =	$642.34		$697.1729	$697.17	$697.15	$697.20