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	$137.73	3.298%	$142.2723	$142.27	$142.25	$142.30
Purchase #2	$131.75	9.318%	$144.0265	$144.03	$144.05	$144.00
Purchase #3	$123.51	3.317%	$127.6068	$127.61	$127.60	$127.60
Purchase #4	$216.95	5.656%	$229.2207	$229.22	$229.20	$229.20
Purchase #5	$127.62	10.873%	$141.4961	$141.50	$141.50	$141.50
Purchase #6	$152.31	5.552%	$160.7663	$160.77	$160.75	$160.80
Purchase #7	$208.85	12.662%	$235.2946	$235.29	$235.30	$235.30
7 purchase totals =	$1,098.72		$1,180.6833	$1,180.69	$1,180.65	$1,180.70