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	$76.53	11.708%	$85.4901	$85.49	$85.50	$85.50
Purchase #2	$48.95	5.326%	$51.5571	$51.56	$51.55	$51.60
Purchase #3	$111.63	13.787%	$127.0204	$127.02	$127.00	$127.00
Purchase #4	$82.90	10.737%	$91.801	$91.80	$91.80	$91.80
Purchase #5	$143.91	3.764%	$149.3268	$149.33	$149.35	$149.30
Purchase #6	$70.78	9.811%	$77.7242	$77.72	$77.70	$77.70
Purchase #7	$91.82	4.437%	$95.8941	$95.89	$95.90	$95.90
7 purchase totals =	$626.52		$678.8137	$678.81	$678.80	$678.80