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	$18.58	6.636%	$19.813	$19.81	$19.80	$19.80
Purchase #2	$67.80	11.698%	$75.7312	$75.73	$75.75	$75.70
Purchase #3	$139.84	8.240%	$151.3628	$151.36	$151.35	$151.40
Purchase #4	$72.46	10.560%	$80.1118	$80.11	$80.10	$80.10
Purchase #5	$45.43	12.772%	$51.2323	$51.23	$51.25	$51.20
Purchase #6	$78.88	13.437%	$89.4791	$89.48	$89.50	$89.50
Purchase #7	$45.74	13.395%	$51.8669	$51.87	$51.85	$51.90
7 purchase totals =	$468.73		$519.5971	$519.59	$519.60	$519.60