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	$38.59	6.501%	$41.0987	$41.10	$41.10	$41.10
Purchase #2	$70.72	3.391%	$73.1181	$73.12	$73.10	$73.10
Purchase #3	$187.87	11.858%	$210.1476	$210.15	$210.15	$210.10
Purchase #4	$194.90	11.619%	$217.5454	$217.55	$217.55	$217.50
Purchase #5	$220.59	4.649%	$230.8452	$230.85	$230.85	$230.80
Purchase #6	$37.66	3.623%	$39.0244	$39.02	$39.00	$39.00
Purchase #7	$146.52	12.558%	$164.92	$164.92	$164.90	$164.90
7 purchase totals =	$896.85		$976.6994	$976.71	$976.65	$976.50