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	$226.28	13.203%	$256.1557	$256.16	$256.15	$256.20
Purchase #2	$97.35	12.323%	$109.3464	$109.35	$109.35	$109.30
Purchase #3	$55.88	3.303%	$57.7257	$57.73	$57.75	$57.70
Purchase #4	$138.54	10.471%	$153.0465	$153.05	$153.05	$153.00
Purchase #5	$93.31	10.454%	$103.0646	$103.06	$103.05	$103.10
Purchase #6	$146.39	12.818%	$165.1543	$165.15	$165.15	$165.20
Purchase #7	$91.97	4.164%	$95.7996	$95.80	$95.80	$95.80
7 purchase totals =	$849.72		$940.2928	$940.30	$940.30	$940.30