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	$90.66	11.103%	$100.726	$100.73	$100.75	$100.70
Purchase #2	$36.26	10.612%	$40.1079	$40.11	$40.10	$40.10
Purchase #3	$233.61	3.659%	$242.1578	$242.16	$242.15	$242.20
Purchase #4	$68.93	13.212%	$78.037	$78.04	$78.05	$78.00
Purchase #5	$159.27	10.402%	$175.8373	$175.84	$175.85	$175.80
Purchase #6	$48.66	12.665%	$54.8228	$54.82	$54.80	$54.80
Purchase #7	$211.75	12.410%	$238.0282	$238.03	$238.05	$238.00
7 purchase totals =	$849.14		$929.7170	$929.73	$929.75	$929.60