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	$159.92	5.422%	$168.5909	$168.59	$168.60	$168.60
Purchase #2	$87.43	11.267%	$97.2807	$97.28	$97.30	$97.30
Purchase #3	$53.62	11.154%	$59.6008	$59.60	$59.60	$59.60
Purchase #4	$139.36	9.208%	$152.1923	$152.19	$152.20	$152.20
Purchase #5	$123.67	11.570%	$137.9786	$137.98	$138.00	$138.00
Purchase #6	$29.62	6.442%	$31.5281	$31.53	$31.55	$31.50
Purchase #7	$225.90	7.163%	$242.0812	$242.08	$242.10	$242.10
7 purchase totals =	$819.52		$889.2526	$889.25	$889.35	$889.30