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	$69.56	12.397%	$78.1834	$78.18	$78.20	$78.20
Purchase #2	$175.52	7.672%	$188.9859	$188.99	$189.00	$189.00
Purchase #3	$93.67	10.153%	$103.1803	$103.18	$103.20	$103.20
Purchase #4	$58.63	12.174%	$65.7676	$65.77	$65.75	$65.80
Purchase #5	$123.75	10.608%	$136.8774	$136.88	$136.90	$136.90
Purchase #6	$154.64	11.832%	$172.937	$172.94	$172.95	$172.90
Purchase #7	$230.48	8.631%	$250.3727	$250.37	$250.35	$250.40
7 purchase totals =	$906.25		$996.3043	$996.31	$996.35	$996.40