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	$89.56	12.304%	$100.5795	$100.58	$100.60	$100.60
Purchase #2	$224.64	7.127%	$240.6501	$240.65	$240.65	$240.70
Purchase #3	$160.94	11.726%	$179.8118	$179.81	$179.80	$179.80
Purchase #4	$12.63	10.366%	$13.9392	$13.94	$13.95	$13.90
Purchase #5	$171.68	7.525%	$184.5989	$184.60	$184.60	$184.60
Purchase #6	$207.79	13.846%	$236.5606	$236.56	$236.55	$236.60
Purchase #7	$38.91	3.713%	$40.3547	$40.35	$40.35	$40.40
7 purchase totals =	$906.15		$996.4948	$996.49	$996.50	$996.60