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	$183.85	8.202%	$198.9294	$198.93	$198.95	$198.90
Purchase #2	$250.26	11.506%	$279.0549	$279.05	$279.05	$279.10
Purchase #3	$87.51	12.551%	$98.4934	$98.49	$98.50	$98.50
Purchase #4	$102.99	7.854%	$111.0788	$111.08	$111.10	$111.10
Purchase #5	$122.81	4.350%	$128.1522	$128.15	$128.15	$128.20
Purchase #6	$182.53	7.864%	$196.8842	$196.88	$196.90	$196.90
Purchase #7	$60.78	11.593%	$67.8262	$67.83	$67.85	$67.80
7 purchase totals =	$990.73		$1,080.4191	$1,080.41	$1,080.50	$1,080.50