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	$160.70	4.656%	$168.1822	$168.18	$168.20	$168.20
Purchase #2	$82.92	8.344%	$89.8388	$89.84	$89.85	$89.80
Purchase #3	$65.83	7.870%	$71.0108	$71.01	$71.00	$71.00
Purchase #4	$215.27	7.592%	$231.6133	$231.61	$231.60	$231.60
Purchase #5	$152.29	5.208%	$160.2213	$160.22	$160.20	$160.20
Purchase #6	$110.81	6.525%	$118.0404	$118.04	$118.05	$118.00
Purchase #7	$74.81	5.566%	$78.9739	$78.97	$78.95	$79.00
7 purchase totals =	$862.63		$917.8807	$917.87	$917.85	$917.80