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	$29.80	4.777%	$31.2235	$31.22	$31.20	$31.20
Purchase #2	$72.64	5.340%	$76.519	$76.52	$76.50	$76.50
Purchase #3	$238.77	3.659%	$247.5066	$247.51	$247.50	$247.50
Purchase #4	$231.68	13.791%	$263.631	$263.63	$263.65	$263.60
Purchase #5	$232.47	9.449%	$254.4361	$254.44	$254.45	$254.40
Purchase #6	$69.29	7.353%	$74.3849	$74.38	$74.40	$74.40
Purchase #7	$90.61	10.669%	$100.2772	$100.28	$100.30	$100.30
7 purchase totals =	$965.26		$1,047.9783	$1,047.98	$1,048.00	$1,047.90