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	$135.96	13.505%	$154.3214	$154.32	$154.30	$154.30
Purchase #2	$38.60	4.320%	$40.2675	$40.27	$40.25	$40.30
Purchase #3	$19.52	10.413%	$21.5526	$21.55	$21.55	$21.60
Purchase #4	$232.43	4.319%	$242.4687	$242.47	$242.45	$242.50
Purchase #5	$176.96	8.397%	$191.8193	$191.82	$191.80	$191.80
Purchase #6	$61.84	7.425%	$66.4316	$66.43	$66.45	$66.40
Purchase #7	$75.89	7.205%	$81.3579	$81.36	$81.35	$81.40
7 purchase totals =	$741.20		$798.2190	$798.22	$798.15	$798.30