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	$53.27	8.112%	$57.5913	$57.59	$57.60	$57.60
Purchase #2	$158.81	5.408%	$167.3984	$167.40	$167.40	$167.40
Purchase #3	$144.49	7.870%	$155.8614	$155.86	$155.85	$155.90
Purchase #4	$122.83	11.604%	$137.0832	$137.08	$137.10	$137.10
Purchase #5	$35.72	9.801%	$39.2209	$39.22	$39.20	$39.20
Purchase #6	$171.72	10.176%	$189.1942	$189.19	$189.20	$189.20
Purchase #7	$83.44	9.184%	$91.1031	$91.10	$91.10	$91.10
7 purchase totals =	$770.28		$837.4525	$837.44	$837.45	$837.50