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	$139.40	8.440%	$151.1654	$151.17	$151.15	$151.20
Purchase #2	$123.86	5.868%	$131.1281	$131.13	$131.15	$131.10
Purchase #3	$182.49	3.546%	$188.9611	$188.96	$188.95	$189.00
Purchase #4	$241.78	13.472%	$274.3526	$274.35	$274.35	$274.40
Purchase #5	$248.45	6.506%	$264.6142	$264.61	$264.60	$264.60
Purchase #6	$61.42	10.706%	$67.9956	$68.00	$68.00	$68.00
Purchase #7	$181.30	4.518%	$189.4911	$189.49	$189.50	$189.50
7 purchase totals =	$1,178.70		$1,267.7081	$1,267.71	$1,267.70	$1,267.80