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	$166.82	6.867%	$178.2755	$178.28	$178.30	$178.30
Purchase #2	$73.82	10.356%	$81.4648	$81.46	$81.45	$81.50
Purchase #3	$38.83	13.294%	$43.9921	$43.99	$44.00	$44.00
Purchase #4	$133.67	8.807%	$145.4423	$145.44	$145.45	$145.40
Purchase #5	$52.80	13.293%	$59.8187	$59.82	$59.80	$59.80
Purchase #6	$38.26	12.609%	$43.0842	$43.08	$43.10	$43.10
Purchase #7	$157.60	11.601%	$175.8832	$175.88	$175.90	$175.90
7 purchase totals =	$661.80		$727.9608	$727.95	$728.00	$728.00