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	$10.82	12.144%	$12.134	$12.13	$12.15	$12.10
Purchase #2	$119.39	3.195%	$123.2045	$123.20	$123.20	$123.20
Purchase #3	$174.33	9.168%	$190.3126	$190.31	$190.30	$190.30
Purchase #4	$181.82	3.619%	$188.4001	$188.40	$188.40	$188.40
Purchase #5	$240.56	5.526%	$253.8533	$253.85	$253.85	$253.90
Purchase #6	$46.92	5.796%	$49.6395	$49.64	$49.65	$49.60
Purchase #7	$62.61	6.648%	$66.7723	$66.77	$66.75	$66.80
7 purchase totals =	$836.45		$884.3163	$884.30	$884.30	$884.30