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	$25.63	12.353%	$28.7961	$28.80	$28.80	$28.80
Purchase #2	$143.28	6.869%	$153.1219	$153.12	$153.10	$153.10
Purchase #3	$184.52	12.850%	$208.2308	$208.23	$208.25	$208.20
Purchase #4	$164.84	4.371%	$172.0452	$172.05	$172.05	$172.00
Purchase #5	$141.25	3.601%	$146.3364	$146.34	$146.35	$146.30
Purchase #6	$88.49	12.839%	$99.8512	$99.85	$99.85	$99.90
Purchase #7	$170.40	10.469%	$188.2392	$188.24	$188.25	$188.20
7 purchase totals =	$918.41		$996.6208	$996.63	$996.65	$996.50