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	$91.27	10.601%	$100.9455	$100.95	$100.95	$100.90
Purchase #2	$233.66	12.711%	$263.3605	$263.36	$263.35	$263.40
Purchase #3	$138.46	4.349%	$144.4816	$144.48	$144.50	$144.50
Purchase #4	$122.62	8.694%	$133.2806	$133.28	$133.30	$133.30
Purchase #5	$13.30	11.298%	$14.8026	$14.80	$14.80	$14.80
Purchase #6	$168.77	9.643%	$185.0445	$185.04	$185.05	$185.00
Purchase #7	$143.42	12.651%	$161.5641	$161.56	$161.55	$161.60
7 purchase totals =	$911.50		$1,003.4794	$1,003.47	$1,003.50	$1,003.50