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	$38.41	4.337%	$40.0758	$40.08	$40.10	$40.10
Purchase #2	$194.38	5.159%	$204.4081	$204.41	$204.40	$204.40
Purchase #3	$79.28	13.440%	$89.9352	$89.94	$89.95	$89.90
Purchase #4	$98.85	9.746%	$108.4839	$108.48	$108.50	$108.50
Purchase #5	$32.70	3.109%	$33.7166	$33.72	$33.70	$33.70
Purchase #6	$74.57	10.853%	$82.6631	$82.66	$82.65	$82.70
Purchase #7	$163.70	3.350%	$169.184	$169.18	$169.20	$169.20
7 purchase totals =	$681.89		$728.4667	$728.47	$728.50	$728.50