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	$51.27	8.777%	$55.77	$55.77	$55.75	$55.80
Purchase #2	$27.34	10.491%	$30.2082	$30.21	$30.20	$30.20
Purchase #3	$37.41	8.301%	$40.5154	$40.52	$40.50	$40.50
Purchase #4	$79.76	12.322%	$89.588	$89.59	$89.60	$89.60
Purchase #5	$151.65	12.252%	$170.2302	$170.23	$170.25	$170.20
Purchase #6	$57.84	9.831%	$63.5263	$63.53	$63.55	$63.50
Purchase #7	$73.34	5.535%	$77.3994	$77.40	$77.40	$77.40
7 purchase totals =	$478.61		$527.2375	$527.25	$527.25	$527.20