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	$222.55	7.288%	$238.7694	$238.77	$238.75	$238.80
Purchase #2	$46.85	5.399%	$49.3794	$49.38	$49.40	$49.40
Purchase #3	$130.52	8.735%	$141.9209	$141.92	$141.90	$141.90
Purchase #4	$153.57	3.317%	$158.6639	$158.66	$158.65	$158.70
Purchase #5	$40.82	11.197%	$45.3906	$45.39	$45.40	$45.40
Purchase #6	$118.36	12.668%	$133.3538	$133.35	$133.35	$133.40
Purchase #7	$198.70	12.123%	$222.7884	$222.79	$222.80	$222.80
7 purchase totals =	$911.37		$990.2664	$990.26	$990.25	$990.40