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	$89.61	11.475%	$99.8927	$99.89	$99.90	$99.90
Purchase #2	$76.59	10.650%	$84.7468	$84.75	$84.75	$84.70
Purchase #3	$95.70	5.206%	$100.6821	$100.68	$100.70	$100.70
Purchase #4	$91.91	8.451%	$99.6773	$99.68	$99.70	$99.70
Purchase #5	$49.42	10.775%	$54.745	$54.75	$54.75	$54.70
Purchase #6	$239.48	6.810%	$255.7886	$255.79	$255.80	$255.80
Purchase #7	$228.60	6.832%	$244.218	$244.22	$244.20	$244.20
7 purchase totals =	$871.31		$939.7505	$939.76	$939.80	$939.70