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	$153.85	7.300%	$165.0811	$165.08	$165.10	$165.10
Purchase #2	$241.45	5.641%	$255.0702	$255.07	$255.05	$255.10
Purchase #3	$48.80	12.172%	$54.7399	$54.74	$54.75	$54.70
Purchase #4	$221.32	5.623%	$233.7648	$233.76	$233.75	$233.80
Purchase #5	$55.65	7.195%	$59.654	$59.65	$59.65	$59.70
Purchase #6	$82.91	13.792%	$94.3449	$94.34	$94.35	$94.30
Purchase #7	$127.40	10.836%	$141.2051	$141.21	$141.20	$141.20
7 purchase totals =	$931.38		$1,003.8600	$1,003.85	$1,003.85	$1,003.90