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	$159.66	6.217%	$169.5861	$169.59	$169.60	$169.60
Purchase #2	$55.78	8.472%	$60.5057	$60.51	$60.50	$60.50
Purchase #3	$231.57	12.849%	$261.3244	$261.32	$261.30	$261.30
Purchase #4	$61.46	11.594%	$68.5857	$68.59	$68.60	$68.60
Purchase #5	$203.30	13.270%	$230.2779	$230.28	$230.30	$230.30
Purchase #6	$209.58	9.679%	$229.8652	$229.87	$229.85	$229.90
Purchase #7	$100.41	11.259%	$111.7152	$111.72	$111.70	$111.70
7 purchase totals =	$1,021.76		$1,131.8602	$1,131.88	$1,131.85	$1,131.90