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	$89.84	12.245%	$100.8409	$100.84	$100.85	$100.80
Purchase #2	$190.91	4.233%	$198.9912	$198.99	$199.00	$199.00
Purchase #3	$136.25	5.131%	$143.241	$143.24	$143.25	$143.20
Purchase #4	$51.95	4.446%	$54.2597	$54.26	$54.25	$54.30
Purchase #5	$96.27	4.399%	$100.5049	$100.50	$100.50	$100.50
Purchase #6	$20.42	4.528%	$21.3446	$21.34	$21.35	$21.30
Purchase #7	$191.26	13.790%	$217.6348	$217.63	$217.65	$217.60
7 purchase totals =	$776.90		$836.8171	$836.80	$836.85	$836.70