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	$51.89	6.531%	$55.2789	$55.28	$55.30	$55.30
Purchase #2	$45.90	11.729%	$51.2836	$51.28	$51.30	$51.30
Purchase #3	$112.92	9.225%	$123.3369	$123.34	$123.35	$123.30
Purchase #4	$222.54	8.799%	$242.1213	$242.12	$242.10	$242.10
Purchase #5	$83.51	6.594%	$89.0166	$89.02	$89.00	$89.00
Purchase #6	$148.38	7.367%	$159.3112	$159.31	$159.30	$159.30
Purchase #7	$137.52	3.362%	$142.1434	$142.14	$142.15	$142.10
7 purchase totals =	$802.66		$862.4919	$862.49	$862.50	$862.40