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	$54.27	6.295%	$57.6863	$57.69	$57.70	$57.70
Purchase #2	$74.46	12.578%	$83.8256	$83.83	$83.85	$83.80
Purchase #3	$136.41	10.464%	$150.6839	$150.68	$150.70	$150.70
Purchase #4	$12.77	13.409%	$14.4823	$14.48	$14.50	$14.50
Purchase #5	$196.78	9.565%	$215.602	$215.60	$215.60	$215.60
Purchase #6	$93.27	12.107%	$104.5622	$104.56	$104.55	$104.60
Purchase #7	$168.74	12.247%	$189.4056	$189.41	$189.40	$189.40
7 purchase totals =	$736.70		$816.2479	$816.25	$816.30	$816.30