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	$183.31	12.436%	$206.1064	$206.11	$206.10	$206.10
Purchase #2	$88.32	3.659%	$91.5516	$91.55	$91.55	$91.60
Purchase #3	$105.61	5.851%	$111.7892	$111.79	$111.80	$111.80
Purchase #4	$47.83	13.390%	$54.2344	$54.23	$54.25	$54.20
Purchase #5	$45.79	7.645%	$49.2906	$49.29	$49.30	$49.30
Purchase #6	$32.96	7.616%	$35.4702	$35.47	$35.45	$35.50
Purchase #7	$15.84	6.871%	$16.9284	$16.93	$16.95	$16.90
7 purchase totals =	$519.66		$565.3708	$565.37	$565.40	$565.40