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	$40.25	6.256%	$42.768	$42.77	$42.75	$42.80
Purchase #2	$34.76	4.808%	$36.4313	$36.43	$36.45	$36.40
Purchase #3	$248.97	10.559%	$275.2587	$275.26	$275.25	$275.30
Purchase #4	$6.87	4.233%	$7.1608	$7.16	$7.15	$7.20
Purchase #5	$159.34	5.317%	$167.8121	$167.81	$167.80	$167.80
Purchase #6	$216.39	5.356%	$227.9798	$227.98	$228.00	$228.00
Purchase #7	$18.96	9.509%	$20.7629	$20.76	$20.75	$20.80
7 purchase totals =	$725.54		$778.1736	$778.17	$778.15	$778.30