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	$85.87	9.654%	$94.1599	$94.16	$94.15	$94.20
Purchase #2	$100.92	12.201%	$113.2332	$113.23	$113.25	$113.20
Purchase #3	$10.58	6.672%	$11.2859	$11.29	$11.30	$11.30
Purchase #4	$80.76	7.767%	$87.0326	$87.03	$87.05	$87.00
Purchase #5	$196.46	7.124%	$210.4558	$210.46	$210.45	$210.50
Purchase #6	$37.32	4.176%	$38.8785	$38.88	$38.90	$38.90
Purchase #7	$80.43	7.140%	$86.1727	$86.17	$86.15	$86.20
7 purchase totals =	$592.34		$641.2186	$641.22	$641.25	$641.30