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	$66.72	5.151%	$70.1567	$70.16	$70.15	$70.20
Purchase #2	$184.25	6.621%	$196.4492	$196.45	$196.45	$196.40
Purchase #3	$243.67	6.594%	$259.7376	$259.74	$259.75	$259.70
Purchase #4	$112.34	12.301%	$126.1589	$126.16	$126.15	$126.20
Purchase #5	$72.84	7.557%	$78.3445	$78.34	$78.35	$78.30
Purchase #6	$39.77	12.581%	$44.7735	$44.77	$44.75	$44.80
Purchase #7	$19.35	13.581%	$21.9779	$21.98	$22.00	$22.00
7 purchase totals =	$738.94		$797.5983	$797.60	$797.60	$797.60