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	$140.91	13.826%	$160.3922	$160.39	$160.40	$160.40
Purchase #2	$112.28	9.855%	$123.3452	$123.35	$123.35	$123.30
Purchase #3	$213.79	12.376%	$240.2487	$240.25	$240.25	$240.20
Purchase #4	$214.74	8.828%	$233.6972	$233.70	$233.70	$233.70
Purchase #5	$55.52	5.413%	$58.5253	$58.53	$58.55	$58.50
Purchase #6	$191.88	3.324%	$198.2581	$198.26	$198.25	$198.30
Purchase #7	$81.65	9.510%	$89.4149	$89.41	$89.40	$89.40
7 purchase totals =	$1,010.77		$1,103.8816	$1,103.89	$1,103.90	$1,103.80