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	$161.57	4.550%	$168.9214	$168.92	$168.90	$168.90
Purchase #2	$27.81	9.840%	$30.5465	$30.55	$30.55	$30.50
Purchase #3	$21.77	10.677%	$24.0944	$24.09	$24.10	$24.10
Purchase #4	$105.69	3.221%	$109.0943	$109.09	$109.10	$109.10
Purchase #5	$220.38	13.573%	$250.2922	$250.29	$250.30	$250.30
Purchase #6	$105.31	8.726%	$114.4994	$114.50	$114.50	$114.50
Purchase #7	$71.88	9.269%	$78.5426	$78.54	$78.55	$78.50
7 purchase totals =	$714.41		$775.9908	$775.98	$776.00	$775.90