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	$169.91	11.361%	$189.2135	$189.21	$189.20	$189.20
Purchase #2	$217.48	5.510%	$229.4631	$229.46	$229.45	$229.50
Purchase #3	$19.82	6.412%	$21.0909	$21.09	$21.10	$21.10
Purchase #4	$64.81	9.342%	$70.8646	$70.86	$70.85	$70.90
Purchase #5	$85.56	4.420%	$89.3418	$89.34	$89.35	$89.30
Purchase #6	$138.52	12.246%	$155.4832	$155.48	$155.50	$155.50
Purchase #7	$32.72	4.761%	$34.2778	$34.28	$34.30	$34.30
7 purchase totals =	$728.82		$789.7349	$789.72	$789.75	$789.80