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	$56.55	3.446%	$58.4987	$58.50	$58.50	$58.50
Purchase #2	$230.48	12.742%	$259.8478	$259.85	$259.85	$259.80
Purchase #3	$218.39	5.488%	$230.3752	$230.38	$230.40	$230.40
Purchase #4	$180.95	10.461%	$199.8792	$199.88	$199.90	$199.90
Purchase #5	$172.85	10.142%	$190.3804	$190.38	$190.40	$190.40
Purchase #6	$124.31	12.536%	$139.8935	$139.89	$139.90	$139.90
Purchase #7	$10.46	7.714%	$11.2669	$11.27	$11.25	$11.30
7 purchase totals =	$993.99		$1,090.1417	$1,090.15	$1,090.20	$1,090.20