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	$80.58	6.148%	$85.5341	$85.53	$85.55	$85.50
Purchase #2	$34.29	13.411%	$38.8886	$38.89	$38.90	$38.90
Purchase #3	$173.72	9.388%	$190.0288	$190.03	$190.05	$190.00
Purchase #4	$249.75	7.569%	$268.6536	$268.65	$268.65	$268.70
Purchase #5	$120.26	6.303%	$127.84	$127.84	$127.85	$127.80
Purchase #6	$74.56	9.721%	$81.808	$81.81	$81.80	$81.80
Purchase #7	$138.56	6.742%	$147.9017	$147.90	$147.90	$147.90
7 purchase totals =	$871.72		$940.6548	$940.65	$940.70	$940.60