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	$246.88	12.573%	$277.9202	$277.92	$277.90	$277.90
Purchase #2	$99.51	13.636%	$113.0792	$113.08	$113.10	$113.10
Purchase #3	$56.81	13.550%	$64.5078	$64.51	$64.50	$64.50
Purchase #4	$45.26	6.489%	$48.1969	$48.20	$48.20	$48.20
Purchase #5	$153.25	12.538%	$172.4645	$172.46	$172.45	$172.50
Purchase #6	$26.46	3.589%	$27.4096	$27.41	$27.40	$27.40
Purchase #7	$233.60	4.284%	$243.6074	$243.61	$243.60	$243.60
7 purchase totals =	$861.77		$947.1856	$947.19	$947.15	$947.20