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	$76.91	7.254%	$82.4891	$82.49	$82.50	$82.50
Purchase #2	$237.55	9.277%	$259.5875	$259.59	$259.60	$259.60
Purchase #3	$64.27	7.158%	$68.8704	$68.87	$68.85	$68.90
Purchase #4	$9.69	3.638%	$10.0425	$10.04	$10.05	$10.00
Purchase #5	$98.54	13.227%	$111.5739	$111.57	$111.55	$111.60
Purchase #6	$25.44	12.357%	$28.5836	$28.58	$28.60	$28.60
Purchase #7	$129.54	7.746%	$139.5742	$139.57	$139.55	$139.60
7 purchase totals =	$641.94		$700.7212	$700.71	$700.70	$700.80