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	$65.97	10.615%	$72.9727	$72.97	$72.95	$73.00
Purchase #2	$246.95	11.196%	$274.5985	$274.60	$274.60	$274.60
Purchase #3	$208.41	3.376%	$215.4459	$215.45	$215.45	$215.40
Purchase #4	$90.29	10.364%	$99.6477	$99.65	$99.65	$99.60
Purchase #5	$43.92	13.332%	$49.7754	$49.78	$49.80	$49.80
Purchase #6	$31.45	4.390%	$32.8307	$32.83	$32.85	$32.80
Purchase #7	$92.60	5.641%	$97.8236	$97.82	$97.80	$97.80
7 purchase totals =	$779.59		$843.0945	$843.10	$843.10	$843.00