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	$64.40	12.568%	$72.4938	$72.49	$72.50	$72.50
Purchase #2	$214.31	13.142%	$242.4746	$242.47	$242.45	$242.50
Purchase #3	$117.30	12.758%	$132.2651	$132.27	$132.25	$132.30
Purchase #4	$138.30	11.243%	$153.8491	$153.85	$153.85	$153.80
Purchase #5	$220.54	10.418%	$243.5159	$243.52	$243.50	$243.50
Purchase #6	$41.36	9.764%	$45.3984	$45.40	$45.40	$45.40
Purchase #7	$25.88	8.678%	$28.1259	$28.13	$28.15	$28.10
7 purchase totals =	$822.09		$918.1228	$918.13	$918.10	$918.10