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	$53.36	9.235%	$58.2878	$58.29	$58.30	$58.30
Purchase #2	$79.92	11.846%	$89.3873	$89.39	$89.40	$89.40
Purchase #3	$53.45	9.529%	$58.5433	$58.54	$58.55	$58.50
Purchase #4	$80.83	5.806%	$85.523	$85.52	$85.50	$85.50
Purchase #5	$127.40	4.368%	$132.9648	$132.96	$132.95	$133.00
Purchase #6	$135.80	6.782%	$145.01	$145.01	$145.00	$145.00
Purchase #7	$90.39	11.189%	$100.5037	$100.50	$100.50	$100.50
7 purchase totals =	$621.15		$670.2199	$670.21	$670.20	$670.20