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	$109.56	5.738%	$115.8466	$115.85	$115.85	$115.80
Purchase #2	$205.55	6.824%	$219.5767	$219.58	$219.60	$219.60
Purchase #3	$95.44	4.172%	$99.4218	$99.42	$99.40	$99.40
Purchase #4	$92.70	13.667%	$105.3693	$105.37	$105.35	$105.40
Purchase #5	$127.52	11.422%	$142.0853	$142.09	$142.10	$142.10
Purchase #6	$181.41	9.440%	$198.5351	$198.54	$198.55	$198.50
Purchase #7	$86.52	6.391%	$92.0495	$92.05	$92.05	$92.00
7 purchase totals =	$898.70		$972.8843	$972.90	$972.90	$972.80