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	$245.71	9.182%	$268.2711	$268.27	$268.25	$268.30
Purchase #2	$144.79	12.660%	$163.1204	$163.12	$163.10	$163.10
Purchase #3	$41.54	8.474%	$45.0601	$45.06	$45.05	$45.10
Purchase #4	$142.84	3.766%	$148.2194	$148.22	$148.20	$148.20
Purchase #5	$57.59	6.855%	$61.5378	$61.54	$61.55	$61.50
Purchase #6	$83.95	7.479%	$90.2286	$90.23	$90.25	$90.20
Purchase #7	$116.58	13.143%	$131.9021	$131.90	$131.90	$131.90
7 purchase totals =	$833.00		$908.3395	$908.34	$908.30	$908.30