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	$60.48	10.656%	$66.9247	$66.92	$66.90	$66.90
Purchase #2	$160.73	4.732%	$168.3357	$168.34	$168.35	$168.30
Purchase #3	$52.85	6.274%	$56.1658	$56.17	$56.15	$56.20
Purchase #4	$146.49	5.553%	$154.6246	$154.62	$154.60	$154.60
Purchase #5	$158.38	8.402%	$171.6871	$171.69	$171.70	$171.70
Purchase #6	$166.85	11.753%	$186.4599	$186.46	$186.45	$186.50
Purchase #7	$146.34	11.175%	$162.6935	$162.69	$162.70	$162.70
7 purchase totals =	$892.12		$966.8913	$966.89	$966.85	$966.90