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	$34.32	13.266%	$38.8729	$38.87	$38.85	$38.90
Purchase #2	$242.94	6.300%	$258.2452	$258.25	$258.25	$258.20
Purchase #3	$8.38	10.603%	$9.2685	$9.27	$9.25	$9.30
Purchase #4	$148.72	7.168%	$159.3802	$159.38	$159.40	$159.40
Purchase #5	$184.34	6.526%	$196.37	$196.37	$196.35	$196.40
Purchase #6	$41.26	6.229%	$43.8301	$43.83	$43.85	$43.80
Purchase #7	$244.64	11.361%	$272.4336	$272.43	$272.45	$272.40
7 purchase totals =	$904.60		$978.4005	$978.40	$978.40	$978.40