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	$37.73	6.685%	$40.2523	$40.25	$40.25	$40.30
Purchase #2	$152.64	12.474%	$171.6803	$171.68	$171.70	$171.70
Purchase #3	$75.62	10.317%	$83.4217	$83.42	$83.40	$83.40
Purchase #4	$136.83	5.457%	$144.2968	$144.30	$144.30	$144.30
Purchase #5	$216.59	5.165%	$227.7769	$227.78	$227.80	$227.80
Purchase #6	$49.68	10.250%	$54.7722	$54.77	$54.75	$54.80
Purchase #7	$133.80	7.460%	$143.7815	$143.78	$143.80	$143.80
7 purchase totals =	$802.89		$865.9817	$865.98	$866.00	$866.10