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	$37.81	12.511%	$42.5404	$42.54	$42.55	$42.50
Purchase #2	$131.48	5.647%	$138.9047	$138.90	$138.90	$138.90
Purchase #3	$100.89	3.333%	$104.2527	$104.25	$104.25	$104.30
Purchase #4	$175.62	9.640%	$192.5498	$192.55	$192.55	$192.50
Purchase #5	$185.27	7.462%	$199.0948	$199.09	$199.10	$199.10
Purchase #6	$129.61	10.528%	$143.2553	$143.26	$143.25	$143.30
Purchase #7	$48.85	10.793%	$54.1224	$54.12	$54.10	$54.10
7 purchase totals =	$809.53		$874.7201	$874.71	$874.70	$874.70