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	$90.98	10.338%	$100.3855	$100.39	$100.40	$100.40
Purchase #2	$190.31	13.409%	$215.8287	$215.83	$215.85	$215.80
Purchase #3	$113.57	4.227%	$118.3706	$118.37	$118.35	$118.40
Purchase #4	$210.74	5.341%	$221.9956	$222.00	$222.00	$222.00
Purchase #5	$207.31	3.843%	$215.2769	$215.28	$215.30	$215.30
Purchase #6	$148.39	12.668%	$167.188	$167.19	$167.20	$167.20
Purchase #7	$34.75	6.733%	$37.0897	$37.09	$37.10	$37.10
7 purchase totals =	$996.05		$1,076.1350	$1,076.15	$1,076.20	$1,076.20