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	$137.43	7.853%	$148.2224	$148.22	$148.20	$148.20
Purchase #2	$185.87	12.692%	$209.4606	$209.46	$209.45	$209.50
Purchase #3	$91.81	10.492%	$101.4427	$101.44	$101.45	$101.40
Purchase #4	$11.59	6.333%	$12.324	$12.32	$12.30	$12.30
Purchase #5	$56.45	13.555%	$64.1018	$64.10	$64.10	$64.10
Purchase #6	$141.46	3.182%	$145.9613	$145.96	$145.95	$146.00
Purchase #7	$68.76	13.487%	$78.0337	$78.03	$78.05	$78.00
7 purchase totals =	$693.37		$759.5465	$759.53	$759.50	$759.50