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	$80.47	10.772%	$89.1382	$89.14	$89.15	$89.10
Purchase #2	$179.40	8.868%	$195.3092	$195.31	$195.30	$195.30
Purchase #3	$92.63	9.611%	$101.5327	$101.53	$101.55	$101.50
Purchase #4	$19.99	4.370%	$20.8636	$20.86	$20.85	$20.90
Purchase #5	$144.73	7.637%	$155.783	$155.78	$155.80	$155.80
Purchase #6	$62.29	13.210%	$70.5185	$70.52	$70.50	$70.50
Purchase #7	$237.94	7.250%	$255.1907	$255.19	$255.20	$255.20
7 purchase totals =	$817.45		$888.3359	$888.33	$888.35	$888.30