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	$21.28	7.561%	$22.889	$22.89	$22.90	$22.90
Purchase #2	$214.70	3.494%	$222.2016	$222.20	$222.20	$222.20
Purchase #3	$185.90	7.819%	$200.4355	$200.44	$200.45	$200.40
Purchase #4	$207.51	9.726%	$227.6924	$227.69	$227.70	$227.70
Purchase #5	$92.33	8.299%	$99.9925	$99.99	$100.00	$100.00
Purchase #6	$240.33	6.478%	$255.8986	$255.90	$255.90	$255.90
Purchase #7	$121.51	12.476%	$136.6696	$136.67	$136.65	$136.70
7 purchase totals =	$1,083.56		$1,165.7792	$1,165.78	$1,165.80	$1,165.80