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	$59.38	11.418%	$66.16	$66.16	$66.15	$66.20
Purchase #2	$167.53	9.690%	$183.7637	$183.76	$183.75	$183.80
Purchase #3	$54.38	12.302%	$61.0698	$61.07	$61.05	$61.10
Purchase #4	$14.94	7.576%	$16.0719	$16.07	$16.05	$16.10
Purchase #5	$112.96	12.435%	$127.0066	$127.01	$127.00	$127.00
Purchase #6	$82.25	9.870%	$90.3681	$90.37	$90.35	$90.40
Purchase #7	$198.46	13.203%	$224.6627	$224.66	$224.65	$224.70
7 purchase totals =	$689.90		$769.1028	$769.10	$769.00	$769.30