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	$144.91	10.170%	$159.6473	$159.65	$159.65	$159.60
Purchase #2	$68.52	5.520%	$72.3023	$72.30	$72.30	$72.30
Purchase #3	$92.41	7.503%	$99.3435	$99.34	$99.35	$99.30
Purchase #4	$109.55	10.273%	$120.8041	$120.80	$120.80	$120.80
Purchase #5	$58.29	13.781%	$66.3229	$66.32	$66.30	$66.30
Purchase #6	$123.60	11.592%	$137.9277	$137.93	$137.95	$137.90
Purchase #7	$145.61	13.394%	$165.113	$165.11	$165.10	$165.10
7 purchase totals =	$742.89		$821.4608	$821.45	$821.45	$821.30