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	$90.51	13.640%	$102.8556	$102.86	$102.85	$102.90
Purchase #2	$70.77	12.754%	$79.796	$79.80	$79.80	$79.80
Purchase #3	$234.39	5.656%	$247.6471	$247.65	$247.65	$247.60
Purchase #4	$12.77	7.239%	$13.6944	$13.69	$13.70	$13.70
Purchase #5	$83.83	7.797%	$90.3662	$90.37	$90.35	$90.40
Purchase #6	$96.64	13.575%	$109.7589	$109.76	$109.75	$109.80
Purchase #7	$145.55	11.152%	$161.7817	$161.78	$161.80	$161.80
7 purchase totals =	$734.46		$805.8999	$805.91	$805.90	$806.00