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	$37.76	12.259%	$42.389	$42.39	$42.40	$42.40
Purchase #2	$233.26	13.200%	$264.0503	$264.05	$264.05	$264.10
Purchase #3	$168.82	5.173%	$177.5531	$177.55	$177.55	$177.60
Purchase #4	$71.48	8.725%	$77.7166	$77.72	$77.70	$77.70
Purchase #5	$49.86	5.772%	$52.7379	$52.74	$52.75	$52.70
Purchase #6	$231.35	10.542%	$255.7389	$255.74	$255.75	$255.70
Purchase #7	$127.42	5.713%	$134.6995	$134.70	$134.70	$134.70
7 purchase totals =	$919.95		$1,004.8853	$1,004.89	$1,004.90	$1,004.90