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	$6.71	12.772%	$7.567	$7.57	$7.55	$7.60
Purchase #2	$61.97	5.316%	$65.2643	$65.26	$65.25	$65.30
Purchase #3	$214.77	8.580%	$233.1973	$233.20	$233.20	$233.20
Purchase #4	$81.87	9.760%	$89.8605	$89.86	$89.85	$89.90
Purchase #5	$183.45	7.322%	$196.8822	$196.88	$196.90	$196.90
Purchase #6	$131.77	6.700%	$140.5986	$140.60	$140.60	$140.60
Purchase #7	$66.71	7.477%	$71.6979	$71.70	$71.70	$71.70
7 purchase totals =	$747.25		$805.0678	$805.07	$805.05	$805.20