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	$41.31	3.651%	$42.8182	$42.82	$42.80	$42.80
Purchase #2	$121.33	7.837%	$130.8386	$130.84	$130.85	$130.80
Purchase #3	$192.59	10.125%	$212.0897	$212.09	$212.10	$212.10
Purchase #4	$157.88	9.249%	$172.4823	$172.48	$172.50	$172.50
Purchase #5	$18.61	12.287%	$20.8966	$20.90	$20.90	$20.90
Purchase #6	$28.41	4.719%	$29.7507	$29.75	$29.75	$29.80
Purchase #7	$43.46	11.406%	$48.417	$48.42	$48.40	$48.40
7 purchase totals =	$603.59		$657.2931	$657.30	$657.30	$657.30