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	$62.82	8.275%	$68.0184	$68.02	$68.00	$68.00
Purchase #2	$123.99	5.692%	$131.0475	$131.05	$131.05	$131.00
Purchase #3	$82.95	9.230%	$90.6063	$90.61	$90.60	$90.60
Purchase #4	$243.96	4.455%	$254.8284	$254.83	$254.85	$254.80
Purchase #5	$99.37	3.841%	$103.1868	$103.19	$103.20	$103.20
Purchase #6	$18.46	8.224%	$19.9782	$19.98	$20.00	$20.00
Purchase #7	$114.82	5.244%	$120.8412	$120.84	$120.85	$120.80
7 purchase totals =	$746.37		$788.5068	$788.52	$788.55	$788.40