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	$45.64	12.254%	$51.2327	$51.23	$51.25	$51.20
Purchase #2	$56.55	5.387%	$59.5963	$59.60	$59.60	$59.60
Purchase #3	$17.97	9.727%	$19.7179	$19.72	$19.70	$19.70
Purchase #4	$64.95	10.677%	$71.8847	$71.88	$71.90	$71.90
Purchase #5	$105.58	10.302%	$116.4569	$116.46	$116.45	$116.50
Purchase #6	$81.90	13.208%	$92.7174	$92.72	$92.70	$92.70
Purchase #7	$88.73	11.342%	$98.7938	$98.79	$98.80	$98.80
7 purchase totals =	$461.32		$510.3997	$510.40	$510.40	$510.40