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	$20.34	5.593%	$21.4776	$21.48	$21.50	$21.50
Purchase #2	$187.65	4.652%	$196.3795	$196.38	$196.40	$196.40
Purchase #3	$95.74	11.402%	$106.6563	$106.66	$106.65	$106.70
Purchase #4	$18.42	5.233%	$19.3839	$19.38	$19.40	$19.40
Purchase #5	$208.44	4.313%	$217.43	$217.43	$217.45	$217.40
Purchase #6	$100.53	4.360%	$104.9131	$104.91	$104.90	$104.90
Purchase #7	$242.71	11.236%	$269.9809	$269.98	$270.00	$270.00
7 purchase totals =	$873.83		$936.2213	$936.22	$936.30	$936.30