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	$151.50	12.784%	$170.8678	$170.87	$170.85	$170.90
Purchase #2	$128.86	12.146%	$144.5113	$144.51	$144.50	$144.50
Purchase #3	$32.32	12.364%	$36.316	$36.32	$36.30	$36.30
Purchase #4	$16.40	13.177%	$18.561	$18.56	$18.55	$18.60
Purchase #5	$59.25	13.174%	$67.0556	$67.06	$67.05	$67.10
Purchase #6	$37.65	13.330%	$42.6687	$42.67	$42.65	$42.70
Purchase #7	$141.92	10.156%	$156.3334	$156.33	$156.35	$156.30
7 purchase totals =	$567.90		$636.3138	$636.32	$636.25	$636.40