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	$180.72	12.312%	$202.9702	$202.97	$202.95	$203.00
Purchase #2	$40.88	11.522%	$45.5902	$45.59	$45.60	$45.60
Purchase #3	$244.27	8.804%	$265.7755	$265.78	$265.80	$265.80
Purchase #4	$39.27	5.568%	$41.4566	$41.46	$41.45	$41.50
Purchase #5	$230.27	7.296%	$247.0705	$247.07	$247.05	$247.10
Purchase #6	$117.86	4.604%	$123.2863	$123.29	$123.30	$123.30
Purchase #7	$134.72	13.740%	$153.2305	$153.23	$153.25	$153.20
7 purchase totals =	$987.99		$1,079.3798	$1,079.39	$1,079.40	$1,079.50