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	$12.26	9.105%	$13.3763	$13.38	$13.40	$13.40
Purchase #2	$67.91	5.266%	$71.4861	$71.49	$71.50	$71.50
Purchase #3	$95.48	4.826%	$100.0879	$100.09	$100.10	$100.10
Purchase #4	$151.43	11.581%	$168.9671	$168.97	$168.95	$169.00
Purchase #5	$83.32	7.467%	$89.5415	$89.54	$89.55	$89.50
Purchase #6	$171.54	3.789%	$178.0397	$178.04	$178.05	$178.00
Purchase #7	$146.49	12.808%	$165.2524	$165.25	$165.25	$165.30
7 purchase totals =	$728.43		$786.7510	$786.76	$786.80	$786.80