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	$6.40	7.402%	$6.8737	$6.87	$6.85	$6.90
Purchase #2	$102.97	8.680%	$111.9078	$111.91	$111.90	$111.90
Purchase #3	$160.76	7.345%	$172.5678	$172.57	$172.55	$172.60
Purchase #4	$69.31	4.723%	$72.5835	$72.58	$72.60	$72.60
Purchase #5	$41.69	12.444%	$46.8779	$46.88	$46.90	$46.90
Purchase #6	$53.49	7.400%	$57.4483	$57.45	$57.45	$57.40
Purchase #7	$236.47	10.269%	$260.7531	$260.75	$260.75	$260.80
7 purchase totals =	$671.09		$729.0121	$729.01	$729.00	$729.10