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	$132.31	5.639%	$139.771	$139.77	$139.75	$139.80
Purchase #2	$31.27	10.152%	$34.4445	$34.44	$34.45	$34.40
Purchase #3	$157.97	5.182%	$166.156	$166.16	$166.15	$166.20
Purchase #4	$61.98	11.852%	$69.3259	$69.33	$69.35	$69.30
Purchase #5	$130.86	13.375%	$148.3625	$148.36	$148.35	$148.40
Purchase #6	$233.93	10.398%	$258.254	$258.25	$258.25	$258.30
Purchase #7	$93.84	5.589%	$99.0847	$99.08	$99.10	$99.10
7 purchase totals =	$842.16		$915.3986	$915.39	$915.40	$915.50