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	$75.97	7.271%	$81.4938	$81.49	$81.50	$81.50
Purchase #2	$102.82	9.609%	$112.7	$112.70	$112.70	$112.70
Purchase #3	$70.52	9.848%	$77.4648	$77.46	$77.45	$77.50
Purchase #4	$65.76	10.478%	$72.6503	$72.65	$72.65	$72.70
Purchase #5	$18.80	5.871%	$19.9037	$19.90	$19.90	$19.90
Purchase #6	$244.83	4.766%	$256.4986	$256.50	$256.50	$256.50
Purchase #7	$107.69	11.840%	$120.4405	$120.44	$120.45	$120.40
7 purchase totals =	$686.39		$741.1517	$741.14	$741.15	$741.20