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	$37.89	5.170%	$39.8489	$39.85	$39.85	$39.80
Purchase #2	$170.72	9.301%	$186.5987	$186.60	$186.60	$186.60
Purchase #3	$94.88	4.475%	$99.1259	$99.13	$99.15	$99.10
Purchase #4	$35.35	12.508%	$39.7716	$39.77	$39.75	$39.80
Purchase #5	$182.40	4.550%	$190.6992	$190.70	$190.70	$190.70
Purchase #6	$140.49	8.314%	$152.1703	$152.17	$152.15	$152.20
Purchase #7	$248.87	6.463%	$264.9545	$264.95	$264.95	$265.00
7 purchase totals =	$910.60		$973.1691	$973.17	$973.15	$973.20