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	$103.51	5.791%	$109.5043	$109.50	$109.50	$109.50
Purchase #2	$100.83	3.274%	$104.1312	$104.13	$104.15	$104.10
Purchase #3	$68.70	7.712%	$73.9981	$74.00	$74.00	$74.00
Purchase #4	$240.56	6.593%	$256.4201	$256.42	$256.40	$256.40
Purchase #5	$79.63	12.496%	$89.5806	$89.58	$89.60	$89.60
Purchase #6	$30.50	11.261%	$33.9346	$33.93	$33.95	$33.90
Purchase #7	$201.29	12.653%	$226.7592	$226.76	$226.75	$226.80
7 purchase totals =	$825.02		$894.3281	$894.32	$894.35	$894.30