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	$85.81	5.485%	$90.5167	$90.52	$90.50	$90.50
Purchase #2	$64.87	13.503%	$73.6294	$73.63	$73.65	$73.60
Purchase #3	$102.32	11.196%	$113.7757	$113.78	$113.80	$113.80
Purchase #4	$34.37	7.330%	$36.8893	$36.89	$36.90	$36.90
Purchase #5	$236.39	10.467%	$261.1329	$261.13	$261.15	$261.10
Purchase #6	$105.69	10.285%	$116.5602	$116.56	$116.55	$116.60
Purchase #7	$225.72	10.830%	$250.1655	$250.17	$250.15	$250.20
7 purchase totals =	$855.17		$942.6697	$942.68	$942.70	$942.70