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	$25.75	8.583%	$27.9601	$27.96	$27.95	$28.00
Purchase #2	$86.73	4.509%	$90.6407	$90.64	$90.65	$90.60
Purchase #3	$43.37	6.277%	$46.0923	$46.09	$46.10	$46.10
Purchase #4	$238.65	10.744%	$264.2906	$264.29	$264.30	$264.30
Purchase #5	$10.56	4.348%	$11.0191	$11.02	$11.00	$11.00
Purchase #6	$171.53	12.253%	$192.5476	$192.55	$192.55	$192.50
Purchase #7	$74.38	11.296%	$82.782	$82.78	$82.80	$82.80
7 purchase totals =	$650.97		$715.3324	$715.33	$715.35	$715.30