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	$56.52	11.798%	$63.1882	$63.19	$63.20	$63.20
Purchase #2	$122.36	4.810%	$128.2455	$128.25	$128.25	$128.20
Purchase #3	$65.51	8.402%	$71.0142	$71.01	$71.00	$71.00
Purchase #4	$134.37	13.684%	$152.7572	$152.76	$152.75	$152.80
Purchase #5	$138.59	9.723%	$152.0651	$152.07	$152.05	$152.10
Purchase #6	$25.90	5.371%	$27.2911	$27.29	$27.30	$27.30
Purchase #7	$151.32	11.204%	$168.2739	$168.27	$168.25	$168.30
7 purchase totals =	$694.57		$762.8352	$762.84	$762.80	$762.90