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	$57.85	5.709%	$61.1527	$61.15	$61.15	$61.20
Purchase #2	$118.59	11.523%	$132.2551	$132.26	$132.25	$132.30
Purchase #3	$51.56	6.538%	$54.931	$54.93	$54.95	$54.90
Purchase #4	$155.31	7.839%	$167.4848	$167.48	$167.50	$167.50
Purchase #5	$81.33	5.848%	$86.0862	$86.09	$86.10	$86.10
Purchase #6	$6.94	10.627%	$7.6775	$7.68	$7.70	$7.70
Purchase #7	$98.60	9.751%	$108.2145	$108.21	$108.20	$108.20
7 purchase totals =	$570.18		$617.8018	$617.80	$617.85	$617.90