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	$144.44	13.566%	$164.0347	$164.03	$164.05	$164.00
Purchase #2	$121.95	5.718%	$128.9231	$128.92	$128.90	$128.90
Purchase #3	$36.92	8.747%	$40.1494	$40.15	$40.15	$40.10
Purchase #4	$101.40	4.265%	$105.7247	$105.72	$105.70	$105.70
Purchase #5	$7.45	5.786%	$7.8811	$7.88	$7.90	$7.90
Purchase #6	$58.94	10.773%	$65.2896	$65.29	$65.30	$65.30
Purchase #7	$79.90	12.175%	$89.6278	$89.63	$89.65	$89.60
7 purchase totals =	$551.00		$601.6304	$601.62	$601.65	$601.50