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	$218.40	9.386%	$238.899	$238.90	$238.90	$238.90
Purchase #2	$243.26	12.168%	$272.8599	$272.86	$272.85	$272.90
Purchase #3	$97.82	8.181%	$105.8227	$105.82	$105.80	$105.80
Purchase #4	$132.84	9.547%	$145.5222	$145.52	$145.50	$145.50
Purchase #5	$55.40	11.476%	$61.7577	$61.76	$61.75	$61.80
Purchase #6	$61.38	3.121%	$63.2957	$63.30	$63.30	$63.30
Purchase #7	$27.88	3.794%	$28.9378	$28.94	$28.95	$28.90
7 purchase totals =	$836.98		$917.0950	$917.10	$917.05	$917.10