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	$18.56	11.413%	$20.6783	$20.68	$20.70	$20.70
Purchase #2	$100.85	5.318%	$106.2132	$106.21	$106.20	$106.20
Purchase #3	$205.56	11.610%	$229.4255	$229.43	$229.45	$229.40
Purchase #4	$229.25	5.323%	$241.453	$241.45	$241.45	$241.50
Purchase #5	$88.56	8.561%	$96.1416	$96.14	$96.15	$96.10
Purchase #6	$53.60	10.600%	$59.2816	$59.28	$59.30	$59.30
Purchase #7	$43.53	4.642%	$45.5507	$45.55	$45.55	$45.60
7 purchase totals =	$739.91		$798.7439	$798.74	$798.80	$798.80