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	$36.76	7.608%	$39.5567	$39.56	$39.55	$39.60
Purchase #2	$143.89	9.150%	$157.0559	$157.06	$157.05	$157.10
Purchase #3	$77.32	5.542%	$81.6051	$81.61	$81.60	$81.60
Purchase #4	$102.35	10.736%	$113.3383	$113.34	$113.35	$113.30
Purchase #5	$164.61	9.297%	$179.9138	$179.91	$179.90	$179.90
Purchase #6	$95.89	13.301%	$108.6443	$108.64	$108.65	$108.60
Purchase #7	$19.49	3.666%	$20.2045	$20.20	$20.20	$20.20
7 purchase totals =	$640.31		$700.3186	$700.32	$700.30	$700.30