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	$172.72	11.319%	$192.2702	$192.27	$192.25	$192.30
Purchase #2	$130.68	13.710%	$148.5962	$148.60	$148.60	$148.60
Purchase #3	$144.42	8.272%	$156.3664	$156.37	$156.35	$156.40
Purchase #4	$31.66	5.126%	$33.2829	$33.28	$33.30	$33.30
Purchase #5	$160.31	11.768%	$179.1753	$179.18	$179.20	$179.20
Purchase #6	$40.63	5.449%	$42.8439	$42.84	$42.85	$42.80
Purchase #7	$68.56	13.674%	$77.9349	$77.93	$77.95	$77.90
7 purchase totals =	$748.98		$830.4698	$830.47	$830.50	$830.50