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	$73.49	6.163%	$78.0192	$78.02	$78.00	$78.00
Purchase #2	$78.85	3.560%	$81.6571	$81.66	$81.65	$81.70
Purchase #3	$25.54	10.801%	$28.2986	$28.30	$28.30	$28.30
Purchase #4	$199.87	12.498%	$224.8498	$224.85	$224.85	$224.80
Purchase #5	$196.84	4.199%	$205.1053	$205.11	$205.10	$205.10
Purchase #6	$140.97	9.121%	$153.8279	$153.83	$153.85	$153.80
Purchase #7	$127.91	7.579%	$137.6043	$137.60	$137.60	$137.60
7 purchase totals =	$843.47		$909.3622	$909.37	$909.35	$909.30