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	$81.63	10.155%	$89.9195	$89.92	$89.90	$89.90
Purchase #2	$145.93	13.657%	$165.8597	$165.86	$165.85	$165.90
Purchase #3	$145.52	13.828%	$165.6425	$165.64	$165.65	$165.60
Purchase #4	$219.63	10.413%	$242.5001	$242.50	$242.50	$242.50
Purchase #5	$175.31	9.786%	$192.4658	$192.47	$192.45	$192.50
Purchase #6	$117.27	12.812%	$132.2946	$132.29	$132.30	$132.30
Purchase #7	$68.42	11.330%	$76.172	$76.17	$76.15	$76.20
7 purchase totals =	$953.71		$1,064.8542	$1,064.85	$1,064.80	$1,064.90