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	$5.61	13.824%	$6.3855	$6.39	$6.40	$6.40
Purchase #2	$81.93	10.853%	$90.8219	$90.82	$90.80	$90.80
Purchase #3	$216.38	13.349%	$245.2646	$245.26	$245.25	$245.30
Purchase #4	$78.48	9.819%	$86.186	$86.19	$86.20	$86.20
Purchase #5	$190.83	10.408%	$210.6916	$210.69	$210.70	$210.70
Purchase #6	$27.57	3.674%	$28.5829	$28.58	$28.60	$28.60
Purchase #7	$199.53	7.522%	$214.5386	$214.54	$214.55	$214.50
7 purchase totals =	$800.33		$882.4711	$882.47	$882.50	$882.50