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	$125.50	13.139%	$141.9894	$141.99	$142.00	$142.00
Purchase #2	$146.39	7.525%	$157.4058	$157.41	$157.40	$157.40
Purchase #3	$41.54	9.822%	$45.6201	$45.62	$45.60	$45.60
Purchase #4	$227.29	12.391%	$255.4535	$255.45	$255.45	$255.50
Purchase #5	$64.37	12.784%	$72.5991	$72.60	$72.60	$72.60
Purchase #6	$30.99	9.126%	$33.8181	$33.82	$33.80	$33.80
Purchase #7	$86.92	4.139%	$90.5176	$90.52	$90.50	$90.50
7 purchase totals =	$723.00		$797.4036	$797.41	$797.35	$797.40