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	$66.68	4.588%	$69.7393	$69.74	$69.75	$69.70
Purchase #2	$238.62	7.635%	$256.8386	$256.84	$256.85	$256.80
Purchase #3	$204.77	12.417%	$230.1963	$230.20	$230.20	$230.20
Purchase #4	$33.78	11.279%	$37.59	$37.59	$37.60	$37.60
Purchase #5	$76.56	11.615%	$85.4524	$85.45	$85.45	$85.50
Purchase #6	$37.39	12.595%	$42.0993	$42.10	$42.10	$42.10
Purchase #7	$69.65	5.528%	$73.5003	$73.50	$73.50	$73.50
7 purchase totals =	$727.45		$795.4162	$795.42	$795.45	$795.40