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	$12.47	4.607%	$13.0445	$13.04	$13.05	$13.00
Purchase #2	$189.95	5.426%	$200.2567	$200.26	$200.25	$200.30
Purchase #3	$164.29	12.585%	$184.9659	$184.97	$184.95	$185.00
Purchase #4	$32.43	12.645%	$36.5308	$36.53	$36.55	$36.50
Purchase #5	$220.64	10.825%	$244.5243	$244.52	$244.50	$244.50
Purchase #6	$96.28	4.106%	$100.2333	$100.23	$100.25	$100.20
Purchase #7	$56.39	9.240%	$61.6004	$61.60	$61.60	$61.60
7 purchase totals =	$772.45		$841.1559	$841.15	$841.15	$841.10