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	$20.55	3.587%	$21.2871	$21.29	$21.30	$21.30
Purchase #2	$186.47	5.580%	$196.875	$196.88	$196.90	$196.90
Purchase #3	$248.43	12.496%	$279.4738	$279.47	$279.45	$279.50
Purchase #4	$119.52	5.754%	$126.3972	$126.40	$126.40	$126.40
Purchase #5	$89.61	12.377%	$100.701	$100.70	$100.70	$100.70
Purchase #6	$172.47	7.764%	$185.8606	$185.86	$185.85	$185.90
Purchase #7	$189.25	10.855%	$209.7931	$209.79	$209.80	$209.80
7 purchase totals =	$1,026.30		$1,120.3878	$1,120.39	$1,120.40	$1,120.50