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	$125.66	10.461%	$138.8053	$138.81	$138.80	$138.80
Purchase #2	$152.67	6.652%	$162.8256	$162.83	$162.85	$162.80
Purchase #3	$187.36	6.184%	$198.9463	$198.95	$198.95	$198.90
Purchase #4	$157.78	13.754%	$179.4811	$179.48	$179.50	$179.50
Purchase #5	$19.46	3.710%	$20.182	$20.18	$20.20	$20.20
Purchase #6	$115.98	10.239%	$127.8552	$127.86	$127.85	$127.90
Purchase #7	$6.27	3.632%	$6.4977	$6.50	$6.50	$6.50
7 purchase totals =	$765.18		$834.5932	$834.61	$834.65	$834.60