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	$71.90	3.626%	$74.5071	$74.51	$74.50	$74.50
Purchase #2	$129.27	12.407%	$145.3085	$145.31	$145.30	$145.30
Purchase #3	$130.25	7.313%	$139.7752	$139.78	$139.80	$139.80
Purchase #4	$177.54	12.868%	$200.3858	$200.39	$200.40	$200.40
Purchase #5	$126.85	12.662%	$142.9117	$142.91	$142.90	$142.90
Purchase #6	$82.41	10.752%	$91.2707	$91.27	$91.25	$91.30
Purchase #7	$92.25	5.747%	$97.5516	$97.55	$97.55	$97.60
7 purchase totals =	$810.47		$891.7106	$891.72	$891.70	$891.80