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	$90.61	12.424%	$101.8674	$101.87	$101.85	$101.90
Purchase #2	$196.75	13.763%	$223.8287	$223.83	$223.85	$223.80
Purchase #3	$20.57	4.716%	$21.5401	$21.54	$21.55	$21.50
Purchase #4	$232.99	3.364%	$240.8278	$240.83	$240.85	$240.80
Purchase #5	$194.79	13.436%	$220.962	$220.96	$220.95	$221.00
Purchase #6	$108.86	3.362%	$112.5199	$112.52	$112.50	$112.50
Purchase #7	$33.70	10.225%	$37.1458	$37.15	$37.15	$37.10
7 purchase totals =	$878.27		$958.6917	$958.70	$958.70	$958.60