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	$192.33	8.420%	$208.5242	$208.52	$208.50	$208.50
Purchase #2	$109.32	12.398%	$122.8735	$122.87	$122.85	$122.90
Purchase #3	$131.37	11.308%	$146.2253	$146.23	$146.25	$146.20
Purchase #4	$195.29	3.617%	$202.3536	$202.35	$202.35	$202.40
Purchase #5	$196.59	6.261%	$208.8985	$208.90	$208.90	$208.90
Purchase #6	$65.32	7.311%	$70.0955	$70.10	$70.10	$70.10
Purchase #7	$18.63	3.462%	$19.275	$19.28	$19.30	$19.30
7 purchase totals =	$908.85		$978.2456	$978.25	$978.25	$978.30