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	$38.92	3.337%	$40.2188	$40.22	$40.20	$40.20
Purchase #2	$123.89	13.690%	$140.8505	$140.85	$140.85	$140.90
Purchase #3	$105.98	11.335%	$117.9928	$117.99	$118.00	$118.00
Purchase #4	$10.78	4.163%	$11.2288	$11.23	$11.25	$11.20
Purchase #5	$194.63	13.816%	$221.5201	$221.52	$221.50	$221.50
Purchase #6	$166.54	13.122%	$188.3934	$188.39	$188.40	$188.40
Purchase #7	$15.37	6.186%	$16.3208	$16.32	$16.30	$16.30
7 purchase totals =	$656.11		$736.5252	$736.52	$736.50	$736.50