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	$37.44	10.621%	$41.4165	$41.42	$41.40	$41.40
Purchase #2	$26.71	5.185%	$28.0949	$28.09	$28.10	$28.10
Purchase #3	$133.73	7.333%	$143.5364	$143.54	$143.55	$143.50
Purchase #4	$13.47	7.781%	$14.5181	$14.52	$14.50	$14.50
Purchase #5	$29.54	10.177%	$32.5463	$32.55	$32.55	$32.50
Purchase #6	$225.34	9.226%	$246.1299	$246.13	$246.15	$246.10
Purchase #7	$44.72	13.551%	$50.78	$50.78	$50.80	$50.80
7 purchase totals =	$510.95		$557.0221	$557.03	$557.05	$556.90