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	$235.61	10.145%	$259.5126	$259.51	$259.50	$259.50
Purchase #2	$162.81	13.570%	$184.9033	$184.90	$184.90	$184.90
Purchase #3	$102.94	8.652%	$111.8464	$111.85	$111.85	$111.80
Purchase #4	$26.35	12.826%	$29.7297	$29.73	$29.75	$29.70
Purchase #5	$219.43	9.569%	$240.4273	$240.43	$240.45	$240.40
Purchase #6	$80.98	9.848%	$88.9549	$88.95	$88.95	$89.00
Purchase #7	$213.47	9.851%	$234.4989	$234.50	$234.50	$234.50
7 purchase totals =	$1,041.59		$1,149.8731	$1,149.87	$1,149.90	$1,149.80