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	$121.55	7.171%	$130.2664	$130.27	$130.25	$130.30
Purchase #2	$135.64	5.301%	$142.8303	$142.83	$142.85	$142.80
Purchase #3	$99.75	5.568%	$105.3041	$105.30	$105.30	$105.30
Purchase #4	$63.84	7.635%	$68.7142	$68.71	$68.70	$68.70
Purchase #5	$68.77	13.163%	$77.8222	$77.82	$77.80	$77.80
Purchase #6	$32.35	4.766%	$33.8918	$33.89	$33.90	$33.90
Purchase #7	$181.38	4.828%	$190.137	$190.14	$190.15	$190.10
7 purchase totals =	$703.28		$748.9660	$748.96	$748.95	$748.90