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	$85.25	6.107%	$90.4562	$90.46	$90.45	$90.50
Purchase #2	$37.54	9.743%	$41.1975	$41.20	$41.20	$41.20
Purchase #3	$173.84	5.177%	$182.8397	$182.84	$182.85	$182.80
Purchase #4	$154.66	7.479%	$166.227	$166.23	$166.25	$166.20
Purchase #5	$210.68	3.103%	$217.2174	$217.22	$217.20	$217.20
Purchase #6	$99.46	4.329%	$103.7656	$103.77	$103.75	$103.80
Purchase #7	$198.90	8.489%	$215.7846	$215.78	$215.80	$215.80
7 purchase totals =	$960.33		$1,017.4880	$1,017.50	$1,017.50	$1,017.50