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	$127.62	10.850%	$141.4668	$141.47	$141.45	$141.50
Purchase #2	$32.72	6.260%	$34.7683	$34.77	$34.75	$34.80
Purchase #3	$104.77	5.703%	$110.745	$110.75	$110.75	$110.70
Purchase #4	$189.98	5.345%	$200.1344	$200.13	$200.15	$200.10
Purchase #5	$153.76	10.161%	$169.3836	$169.38	$169.40	$169.40
Purchase #6	$69.51	12.251%	$78.0257	$78.03	$78.05	$78.00
Purchase #7	$42.82	12.757%	$48.2825	$48.28	$48.30	$48.30
7 purchase totals =	$721.18		$782.8063	$782.81	$782.85	$782.80