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	$237.65	7.673%	$255.8849	$255.88	$255.90	$255.90
Purchase #2	$39.92	5.413%	$42.0809	$42.08	$42.10	$42.10
Purchase #3	$149.53	8.442%	$162.1533	$162.15	$162.15	$162.20
Purchase #4	$187.98	11.779%	$210.1222	$210.12	$210.10	$210.10
Purchase #5	$84.86	10.789%	$94.0155	$94.02	$94.00	$94.00
Purchase #6	$87.54	6.779%	$93.4743	$93.47	$93.45	$93.50
Purchase #7	$133.40	13.301%	$151.1435	$151.14	$151.15	$151.10
7 purchase totals =	$920.88		$1,008.8746	$1,008.86	$1,008.85	$1,008.90