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	$48.75	9.174%	$53.2223	$53.22	$53.20	$53.20
Purchase #2	$184.72	10.564%	$204.2338	$204.23	$204.25	$204.20
Purchase #3	$92.83	11.603%	$103.6011	$103.60	$103.60	$103.60
Purchase #4	$102.83	10.725%	$113.8585	$113.86	$113.85	$113.90
Purchase #5	$243.73	13.136%	$275.7464	$275.75	$275.75	$275.70
Purchase #6	$139.57	11.387%	$155.4628	$155.46	$155.45	$155.50
Purchase #7	$10.57	7.529%	$11.3658	$11.37	$11.35	$11.40
7 purchase totals =	$823.00		$917.4907	$917.49	$917.45	$917.50