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	$51.54	5.717%	$54.4865	$54.49	$54.50	$54.50
Purchase #2	$133.80	4.304%	$139.5588	$139.56	$139.55	$139.60
Purchase #3	$101.55	8.192%	$109.869	$109.87	$109.85	$109.90
Purchase #4	$27.53	7.758%	$29.6658	$29.67	$29.65	$29.70
Purchase #5	$98.94	4.526%	$103.418	$103.42	$103.40	$103.40
Purchase #6	$15.87	13.874%	$18.0718	$18.07	$18.05	$18.10
Purchase #7	$76.83	6.695%	$81.9738	$81.97	$81.95	$82.00
7 purchase totals =	$506.06		$537.0437	$537.05	$536.95	$537.20