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	$79.94	11.380%	$89.0372	$89.04	$89.05	$89.00
Purchase #2	$169.93	6.142%	$180.3671	$180.37	$180.35	$180.40
Purchase #3	$156.68	9.863%	$172.1333	$172.13	$172.15	$172.10
Purchase #4	$26.58	10.629%	$29.4052	$29.41	$29.40	$29.40
Purchase #5	$123.35	6.659%	$131.5639	$131.56	$131.55	$131.60
Purchase #6	$60.96	13.428%	$69.1457	$69.15	$69.15	$69.10
Purchase #7	$44.41	4.244%	$46.2948	$46.29	$46.30	$46.30
7 purchase totals =	$661.85		$717.9472	$717.95	$717.95	$717.90