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	$99.34	6.779%	$106.0743	$106.07	$106.05	$106.10
Purchase #2	$224.97	13.863%	$256.1576	$256.16	$256.15	$256.20
Purchase #3	$56.54	8.189%	$61.1701	$61.17	$61.15	$61.20
Purchase #4	$37.41	13.184%	$42.3421	$42.34	$42.35	$42.30
Purchase #5	$125.94	11.682%	$140.6523	$140.65	$140.65	$140.70
Purchase #6	$23.58	9.860%	$25.905	$25.91	$25.90	$25.90
Purchase #7	$213.99	4.268%	$223.1231	$223.12	$223.10	$223.10
7 purchase totals =	$781.77		$855.4245	$855.42	$855.35	$855.50