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	$17.86	10.350%	$19.7085	$19.71	$19.70	$19.70
Purchase #2	$100.59	9.203%	$109.8473	$109.85	$109.85	$109.80
Purchase #3	$200.42	11.121%	$222.7087	$222.71	$222.70	$222.70
Purchase #4	$184.27	11.308%	$205.1073	$205.11	$205.10	$205.10
Purchase #5	$92.85	6.810%	$99.1731	$99.17	$99.15	$99.20
Purchase #6	$202.25	4.684%	$211.7234	$211.72	$211.70	$211.70
Purchase #7	$12.57	8.521%	$13.6411	$13.64	$13.65	$13.60
7 purchase totals =	$810.81		$881.9094	$881.91	$881.85	$881.80