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	$189.72	4.636%	$198.5154	$198.52	$198.50	$198.50
Purchase #2	$231.25	8.487%	$250.8762	$250.88	$250.90	$250.90
Purchase #3	$189.72	13.346%	$215.04	$215.04	$215.05	$215.00
Purchase #4	$30.28	13.791%	$34.4559	$34.46	$34.45	$34.50
Purchase #5	$32.79	7.238%	$35.1633	$35.16	$35.15	$35.20
Purchase #6	$14.95	6.781%	$15.9638	$15.96	$15.95	$16.00
Purchase #7	$52.28	13.104%	$59.1308	$59.13	$59.15	$59.10
7 purchase totals =	$740.99		$809.1454	$809.15	$809.15	$809.20