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	$177.72	7.183%	$190.4856	$190.49	$190.50	$190.50
Purchase #2	$169.45	10.675%	$187.5388	$187.54	$187.55	$187.50
Purchase #3	$220.50	9.763%	$242.0274	$242.03	$242.05	$242.00
Purchase #4	$77.97	3.745%	$80.89	$80.89	$80.90	$80.90
Purchase #5	$18.84	6.225%	$20.0128	$20.01	$20.00	$20.00
Purchase #6	$52.53	4.301%	$54.7893	$54.79	$54.80	$54.80
Purchase #7	$60.66	6.140%	$64.3845	$64.38	$64.40	$64.40
7 purchase totals =	$777.67		$840.1284	$840.13	$840.20	$840.10