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	$152.64	4.693%	$159.8034	$159.80	$159.80	$159.80
Purchase #2	$81.28	11.311%	$90.4736	$90.47	$90.45	$90.50
Purchase #3	$41.72	9.699%	$45.7664	$45.77	$45.75	$45.80
Purchase #4	$129.26	10.685%	$143.0714	$143.07	$143.05	$143.10
Purchase #5	$219.74	12.465%	$247.1306	$247.13	$247.15	$247.10
Purchase #6	$138.40	6.413%	$147.2756	$147.28	$147.30	$147.30
Purchase #7	$32.62	8.586%	$35.4208	$35.42	$35.40	$35.40
7 purchase totals =	$795.66		$868.9418	$868.94	$868.90	$869.00