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	$70.62	10.202%	$77.8247	$77.82	$77.80	$77.80
Purchase #2	$34.78	7.654%	$37.4421	$37.44	$37.45	$37.40
Purchase #3	$246.40	6.608%	$262.6821	$262.68	$262.70	$262.70
Purchase #4	$146.93	5.602%	$155.161	$155.16	$155.15	$155.20
Purchase #5	$28.60	9.849%	$31.4168	$31.42	$31.40	$31.40
Purchase #6	$54.79	3.152%	$56.517	$56.52	$56.50	$56.50
Purchase #7	$152.37	12.478%	$171.3827	$171.38	$171.40	$171.40
7 purchase totals =	$734.49		$792.4264	$792.42	$792.40	$792.40