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	$83.43	6.533%	$88.8805	$88.88	$88.90	$88.90
Purchase #2	$41.35	7.134%	$44.2999	$44.30	$44.30	$44.30
Purchase #3	$142.94	7.197%	$153.2274	$153.23	$153.25	$153.20
Purchase #4	$43.78	3.573%	$45.3443	$45.34	$45.35	$45.30
Purchase #5	$82.61	12.308%	$92.7776	$92.78	$92.80	$92.80
Purchase #6	$65.43	7.874%	$70.582	$70.58	$70.60	$70.60
Purchase #7	$242.94	5.305%	$255.828	$255.83	$255.85	$255.80
7 purchase totals =	$702.48		$750.9397	$750.94	$751.05	$750.90