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	$248.26	12.321%	$278.8481	$278.85	$278.85	$278.80
Purchase #2	$54.74	11.794%	$61.196	$61.20	$61.20	$61.20
Purchase #3	$188.89	4.741%	$197.8453	$197.85	$197.85	$197.80
Purchase #4	$91.72	8.451%	$99.4713	$99.47	$99.45	$99.50
Purchase #5	$49.30	6.774%	$52.6396	$52.64	$52.65	$52.60
Purchase #6	$38.40	6.424%	$40.8668	$40.87	$40.85	$40.90
Purchase #7	$29.67	8.871%	$32.302	$32.30	$32.30	$32.30
7 purchase totals =	$700.98		$763.1691	$763.18	$763.15	$763.10