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	$58.31	13.328%	$66.0816	$66.08	$66.10	$66.10
Purchase #2	$223.52	3.515%	$231.3767	$231.38	$231.40	$231.40
Purchase #3	$12.35	6.262%	$13.1234	$13.12	$13.10	$13.10
Purchase #4	$188.34	4.224%	$196.2955	$196.30	$196.30	$196.30
Purchase #5	$24.51	10.800%	$27.1571	$27.16	$27.15	$27.20
Purchase #6	$244.97	4.834%	$256.8118	$256.81	$256.80	$256.80
Purchase #7	$145.50	9.800%	$159.759	$159.76	$159.75	$159.80
7 purchase totals =	$897.50		$950.6051	$950.61	$950.60	$950.70