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	$54.37	12.691%	$61.2701	$61.27	$61.25	$61.30
Purchase #2	$105.34	6.104%	$111.77	$111.77	$111.75	$111.80
Purchase #3	$133.36	4.244%	$139.0198	$139.02	$139.00	$139.00
Purchase #4	$215.55	8.756%	$234.4236	$234.42	$234.40	$234.40
Purchase #5	$71.91	4.603%	$75.22	$75.22	$75.20	$75.20
Purchase #6	$109.31	7.287%	$117.2754	$117.28	$117.30	$117.30
Purchase #7	$137.80	11.328%	$153.41	$153.41	$153.40	$153.40
7 purchase totals =	$827.64		$892.3889	$892.39	$892.30	$892.40