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	$64.56	6.445%	$68.7209	$68.72	$68.70	$68.70
Purchase #2	$100.93	13.191%	$114.2437	$114.24	$114.25	$114.20
Purchase #3	$37.60	13.331%	$42.6125	$42.61	$42.60	$42.60
Purchase #4	$80.99	5.598%	$85.5238	$85.52	$85.50	$85.50
Purchase #5	$58.85	11.621%	$65.689	$65.69	$65.70	$65.70
Purchase #6	$218.52	6.703%	$233.1674	$233.17	$233.15	$233.20
Purchase #7	$201.91	12.166%	$226.4744	$226.47	$226.45	$226.50
7 purchase totals =	$763.36		$836.4317	$836.42	$836.35	$836.40