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	$223.41	3.771%	$231.8348	$231.83	$231.85	$231.80
Purchase #2	$193.29	5.159%	$203.2618	$203.26	$203.25	$203.30
Purchase #3	$10.90	11.667%	$12.1717	$12.17	$12.15	$12.20
Purchase #4	$108.96	3.305%	$112.5611	$112.56	$112.55	$112.60
Purchase #5	$132.76	4.334%	$138.5138	$138.51	$138.50	$138.50
Purchase #6	$250.76	12.541%	$282.2078	$282.21	$282.20	$282.20
Purchase #7	$96.51	4.172%	$100.5364	$100.54	$100.55	$100.50
7 purchase totals =	$1,016.59		$1,081.0874	$1,081.08	$1,081.05	$1,081.10