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	$156.89	5.568%	$165.6256	$165.63	$165.65	$165.60
Purchase #2	$72.76	8.286%	$78.7889	$78.79	$78.80	$78.80
Purchase #3	$112.82	10.401%	$124.5544	$124.55	$124.55	$124.60
Purchase #4	$104.60	8.213%	$113.1908	$113.19	$113.20	$113.20
Purchase #5	$240.48	10.130%	$264.8406	$264.84	$264.85	$264.80
Purchase #6	$129.52	10.364%	$142.9435	$142.94	$142.95	$142.90
Purchase #7	$13.83	12.106%	$15.5043	$15.50	$15.50	$15.50
7 purchase totals =	$830.90		$905.4481	$905.44	$905.50	$905.40