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	$160.68	6.508%	$171.1371	$171.14	$171.15	$171.10
Purchase #2	$19.29	7.246%	$20.6878	$20.69	$20.70	$20.70
Purchase #3	$86.97	3.396%	$89.9235	$89.92	$89.90	$89.90
Purchase #4	$36.41	4.850%	$38.1759	$38.18	$38.20	$38.20
Purchase #5	$199.25	7.489%	$214.1718	$214.17	$214.15	$214.20
Purchase #6	$18.54	9.405%	$20.2837	$20.28	$20.30	$20.30
Purchase #7	$85.62	8.225%	$92.6622	$92.66	$92.65	$92.70
7 purchase totals =	$606.76		$647.0420	$647.04	$647.05	$647.10