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	$169.81	12.350%	$190.7815	$190.78	$190.80	$190.80
Purchase #2	$64.50	4.626%	$67.4838	$67.48	$67.50	$67.50
Purchase #3	$81.73	12.511%	$91.9552	$91.96	$91.95	$92.00
Purchase #4	$46.78	6.152%	$49.6579	$49.66	$49.65	$49.70
Purchase #5	$18.34	4.125%	$19.0965	$19.10	$19.10	$19.10
Purchase #6	$34.26	12.499%	$38.5422	$38.54	$38.55	$38.50
Purchase #7	$71.81	12.483%	$80.774	$80.77	$80.75	$80.80
7 purchase totals =	$487.23		$538.2911	$538.29	$538.30	$538.40