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	$5.30	3.653%	$5.4936	$5.49	$5.50	$5.50
Purchase #2	$37.92	11.172%	$42.1564	$42.16	$42.15	$42.20
Purchase #3	$55.93	4.582%	$58.4927	$58.49	$58.50	$58.50
Purchase #4	$143.39	7.127%	$153.6094	$153.61	$153.60	$153.60
Purchase #5	$250.96	4.783%	$262.9634	$262.96	$262.95	$263.00
Purchase #6	$150.36	10.579%	$166.2666	$166.27	$166.25	$166.30
Purchase #7	$208.90	4.170%	$217.6111	$217.61	$217.60	$217.60
7 purchase totals =	$852.76		$906.5932	$906.59	$906.55	$906.70