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	$10.50	12.717%	$11.8353	$11.84	$11.85	$11.80
Purchase #2	$50.78	12.321%	$57.0366	$57.04	$57.05	$57.00
Purchase #3	$154.35	10.662%	$170.8068	$170.81	$170.80	$170.80
Purchase #4	$245.34	7.784%	$264.4373	$264.44	$264.45	$264.40
Purchase #5	$82.83	12.529%	$93.2078	$93.21	$93.20	$93.20
Purchase #6	$29.40	11.474%	$32.7734	$32.77	$32.75	$32.80
Purchase #7	$78.40	5.217%	$82.4901	$82.49	$82.50	$82.50
7 purchase totals =	$651.60		$712.5873	$712.60	$712.60	$712.50