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	$204.86	12.828%	$231.1394	$231.14	$231.15	$231.10
Purchase #2	$45.62	6.398%	$48.5388	$48.54	$48.55	$48.50
Purchase #3	$210.25	13.271%	$238.1523	$238.15	$238.15	$238.20
Purchase #4	$231.62	10.746%	$256.5099	$256.51	$256.50	$256.50
Purchase #5	$81.97	12.380%	$92.1179	$92.12	$92.10	$92.10
Purchase #6	$47.87	4.470%	$50.0098	$50.01	$50.00	$50.00
Purchase #7	$122.44	13.621%	$139.1176	$139.12	$139.10	$139.10
7 purchase totals =	$944.63		$1,055.5857	$1,055.59	$1,055.55	$1,055.50