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	$151.43	8.783%	$164.7301	$164.73	$164.75	$164.70
Purchase #2	$44.49	12.558%	$50.0771	$50.08	$50.10	$50.10
Purchase #3	$250.47	12.680%	$282.2296	$282.23	$282.25	$282.20
Purchase #4	$52.46	11.742%	$58.6199	$58.62	$58.60	$58.60
Purchase #5	$94.34	9.317%	$103.1297	$103.13	$103.15	$103.10
Purchase #6	$68.74	12.760%	$77.5112	$77.51	$77.50	$77.50
Purchase #7	$65.63	10.578%	$72.5723	$72.57	$72.55	$72.60
7 purchase totals =	$727.56		$808.8699	$808.87	$808.90	$808.80