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	$47.92	10.256%	$52.8347	$52.83	$52.85	$52.80
Purchase #2	$197.89	12.553%	$222.7311	$222.73	$222.75	$222.70
Purchase #3	$103.57	7.783%	$111.6309	$111.63	$111.65	$111.60
Purchase #4	$151.53	9.269%	$165.5753	$165.58	$165.60	$165.60
Purchase #5	$172.84	10.562%	$191.0954	$191.10	$191.10	$191.10
Purchase #6	$181.85	9.380%	$198.9075	$198.91	$198.90	$198.90
Purchase #7	$129.98	12.182%	$145.8142	$145.81	$145.80	$145.80
7 purchase totals =	$985.58		$1,088.5891	$1,088.59	$1,088.65	$1,088.50