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	$8.86	13.135%	$10.0238	$10.02	$10.00	$10.00
Purchase #2	$154.60	9.521%	$169.3195	$169.32	$169.30	$169.30
Purchase #3	$240.85	6.236%	$255.8694	$255.87	$255.85	$255.90
Purchase #4	$112.85	5.327%	$118.8615	$118.86	$118.85	$118.90
Purchase #5	$50.77	13.583%	$57.6661	$57.67	$57.65	$57.70
Purchase #6	$209.46	7.729%	$225.6492	$225.65	$225.65	$225.60
Purchase #7	$59.97	4.760%	$62.8246	$62.82	$62.80	$62.80
7 purchase totals =	$837.36		$900.2141	$900.21	$900.10	$900.20