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	$99.61	10.258%	$109.828	$109.83	$109.85	$109.80
Purchase #2	$143.60	8.136%	$155.2833	$155.28	$155.30	$155.30
Purchase #3	$119.44	9.304%	$130.5527	$130.55	$130.55	$130.60
Purchase #4	$123.81	5.470%	$130.5824	$130.58	$130.60	$130.60
Purchase #5	$61.30	11.764%	$68.5113	$68.51	$68.50	$68.50
Purchase #6	$109.27	13.373%	$123.8827	$123.88	$123.90	$123.90
Purchase #7	$44.63	9.370%	$48.8118	$48.81	$48.80	$48.80
7 purchase totals =	$701.66		$767.4522	$767.44	$767.50	$767.50