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	$80.47	12.807%	$90.7758	$90.78	$90.80	$90.80
Purchase #2	$94.35	10.804%	$104.5436	$104.54	$104.55	$104.50
Purchase #3	$245.47	13.760%	$279.2467	$279.25	$279.25	$279.20
Purchase #4	$231.31	7.783%	$249.3129	$249.31	$249.30	$249.30
Purchase #5	$18.49	7.437%	$19.8651	$19.87	$19.85	$19.90
Purchase #6	$51.66	9.721%	$56.6819	$56.68	$56.70	$56.70
Purchase #7	$80.56	7.429%	$86.5448	$86.54	$86.55	$86.50
7 purchase totals =	$802.31		$886.9708	$886.97	$887.00	$886.90