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	$36.60	5.166%	$38.4908	$38.49	$38.50	$38.50
Purchase #2	$183.51	13.517%	$208.315	$208.32	$208.30	$208.30
Purchase #3	$216.54	10.191%	$238.6076	$238.61	$238.60	$238.60
Purchase #4	$231.27	8.497%	$250.921	$250.92	$250.90	$250.90
Purchase #5	$226.54	9.302%	$247.6128	$247.61	$247.60	$247.60
Purchase #6	$93.49	7.292%	$100.3073	$100.31	$100.30	$100.30
Purchase #7	$194.94	13.339%	$220.943	$220.94	$220.95	$220.90
7 purchase totals =	$1,182.89		$1,305.1975	$1,305.20	$1,305.15	$1,305.10