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	$135.52	12.630%	$152.6362	$152.64	$152.65	$152.60
Purchase #2	$108.66	7.715%	$117.0431	$117.04	$117.05	$117.00
Purchase #3	$91.31	13.631%	$103.7565	$103.76	$103.75	$103.80
Purchase #4	$57.44	12.494%	$64.6166	$64.62	$64.60	$64.60
Purchase #5	$9.37	12.837%	$10.5728	$10.57	$10.55	$10.60
Purchase #6	$94.34	5.614%	$99.6362	$99.64	$99.65	$99.60
Purchase #7	$79.45	12.771%	$89.5966	$89.60	$89.60	$89.60
7 purchase totals =	$576.09		$637.8580	$637.87	$637.85	$637.80