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	$87.50	13.602%	$99.4018	$99.40	$99.40	$99.40
Purchase #2	$84.84	12.341%	$95.3101	$95.31	$95.30	$95.30
Purchase #3	$200.78	10.606%	$222.0747	$222.07	$222.05	$222.10
Purchase #4	$201.61	4.605%	$210.8941	$210.89	$210.90	$210.90
Purchase #5	$88.52	8.707%	$96.2274	$96.23	$96.25	$96.20
Purchase #6	$6.44	10.623%	$7.1241	$7.12	$7.10	$7.10
Purchase #7	$161.77	11.574%	$180.4933	$180.49	$180.50	$180.50
7 purchase totals =	$831.46		$911.5255	$911.51	$911.50	$911.50