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	$207.45	12.747%	$233.8937	$233.89	$233.90	$233.90
Purchase #2	$38.90	9.625%	$42.6441	$42.64	$42.65	$42.60
Purchase #3	$168.68	8.654%	$183.2776	$183.28	$183.30	$183.30
Purchase #4	$234.89	12.707%	$264.7375	$264.74	$264.75	$264.70
Purchase #5	$132.59	11.847%	$148.2979	$148.30	$148.30	$148.30
Purchase #6	$78.38	6.344%	$83.3524	$83.35	$83.35	$83.40
Purchase #7	$37.61	9.589%	$41.2164	$41.22	$41.20	$41.20
7 purchase totals =	$898.50		$997.4196	$997.42	$997.45	$997.40