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	$28.76	8.676%	$31.2552	$31.26	$31.25	$31.30
Purchase #2	$118.90	9.603%	$130.318	$130.32	$130.30	$130.30
Purchase #3	$240.67	5.441%	$253.7649	$253.76	$253.75	$253.80
Purchase #4	$151.54	13.578%	$172.1161	$172.12	$172.10	$172.10
Purchase #5	$138.96	10.471%	$153.5105	$153.51	$153.50	$153.50
Purchase #6	$38.49	12.697%	$43.3771	$43.38	$43.40	$43.40
Purchase #7	$72.46	7.359%	$77.7923	$77.79	$77.80	$77.80
7 purchase totals =	$789.78		$862.1341	$862.14	$862.10	$862.20