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	$31.71	5.474%	$33.4458	$33.45	$33.45	$33.40
Purchase #2	$146.71	5.596%	$154.9199	$154.92	$154.90	$154.90
Purchase #3	$140.39	3.290%	$145.0088	$145.01	$145.00	$145.00
Purchase #4	$101.96	7.162%	$109.2624	$109.26	$109.25	$109.30
Purchase #5	$129.73	13.415%	$147.1333	$147.13	$147.15	$147.10
Purchase #6	$139.62	12.156%	$156.5922	$156.59	$156.60	$156.60
Purchase #7	$67.31	10.716%	$74.5229	$74.52	$74.50	$74.50
7 purchase totals =	$757.43		$820.8853	$820.88	$820.85	$820.80