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	$112.75	6.784%	$120.399	$120.40	$120.40	$120.40
Purchase #2	$61.49	6.160%	$65.2778	$65.28	$65.30	$65.30
Purchase #3	$7.57	5.438%	$7.9817	$7.98	$8.00	$8.00
Purchase #4	$153.38	13.301%	$173.7811	$173.78	$173.80	$173.80
Purchase #5	$89.88	10.558%	$99.3695	$99.37	$99.35	$99.40
Purchase #6	$182.36	5.732%	$192.8129	$192.81	$192.80	$192.80
Purchase #7	$90.89	10.647%	$100.5671	$100.57	$100.55	$100.60
7 purchase totals =	$698.32		$760.1891	$760.19	$760.20	$760.30