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	$61.29	9.696%	$67.2327	$67.23	$67.25	$67.20
Purchase #2	$126.82	7.507%	$136.3404	$136.34	$136.35	$136.30
Purchase #3	$35.65	10.699%	$39.4642	$39.46	$39.45	$39.50
Purchase #4	$56.83	7.306%	$60.982	$60.98	$61.00	$61.00
Purchase #5	$36.99	3.684%	$38.3527	$38.35	$38.35	$38.40
Purchase #6	$126.34	10.672%	$139.823	$139.82	$139.80	$139.80
Purchase #7	$177.64	11.652%	$198.3386	$198.34	$198.35	$198.30
7 purchase totals =	$621.56		$680.5336	$680.52	$680.55	$680.50