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	$67.41	5.205%	$70.9187	$70.92	$70.90	$70.90
Purchase #2	$180.96	13.874%	$206.0664	$206.07	$206.05	$206.10
Purchase #3	$50.83	7.216%	$54.4979	$54.50	$54.50	$54.50
Purchase #4	$130.26	11.374%	$145.0758	$145.08	$145.10	$145.10
Purchase #5	$56.40	5.313%	$59.3965	$59.40	$59.40	$59.40
Purchase #6	$176.47	4.386%	$184.21	$184.21	$184.20	$184.20
Purchase #7	$182.60	4.425%	$190.6801	$190.68	$190.70	$190.70
7 purchase totals =	$844.93		$910.8454	$910.86	$910.85	$910.90