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	$75.52	9.619%	$82.7843	$82.78	$82.80	$82.80
Purchase #2	$39.96	5.233%	$42.0511	$42.05	$42.05	$42.10
Purchase #3	$127.78	5.551%	$134.8731	$134.87	$134.85	$134.90
Purchase #4	$13.26	9.286%	$14.4913	$14.49	$14.50	$14.50
Purchase #5	$36.57	10.425%	$40.3824	$40.38	$40.40	$40.40
Purchase #6	$146.48	7.702%	$157.7619	$157.76	$157.75	$157.80
Purchase #7	$125.99	10.679%	$139.4445	$139.44	$139.45	$139.40
7 purchase totals =	$565.56		$611.7886	$611.77	$611.80	$611.90