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	$184.69	3.571%	$191.2853	$191.29	$191.30	$191.30
Purchase #2	$31.67	7.761%	$34.1279	$34.13	$34.15	$34.10
Purchase #3	$38.89	8.468%	$42.1832	$42.18	$42.20	$42.20
Purchase #4	$122.32	4.478%	$127.7975	$127.80	$127.80	$127.80
Purchase #5	$145.61	6.674%	$155.328	$155.33	$155.35	$155.30
Purchase #6	$236.83	13.569%	$268.9655	$268.97	$268.95	$269.00
Purchase #7	$10.60	5.476%	$11.1805	$11.18	$11.20	$11.20
7 purchase totals =	$770.61		$830.8679	$830.88	$830.95	$830.90