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	$144.35	8.450%	$156.5476	$156.55	$156.55	$156.50
Purchase #2	$124.75	5.554%	$131.6786	$131.68	$131.70	$131.70
Purchase #3	$227.27	3.256%	$234.6699	$234.67	$234.65	$234.70
Purchase #4	$79.64	11.552%	$88.84	$88.84	$88.85	$88.80
Purchase #5	$80.42	8.648%	$87.3747	$87.37	$87.35	$87.40
Purchase #6	$115.82	13.846%	$131.8564	$131.86	$131.85	$131.90
Purchase #7	$51.90	10.787%	$57.4985	$57.50	$57.50	$57.50
7 purchase totals =	$824.15		$888.4657	$888.47	$888.45	$888.50