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	$241.93	5.621%	$255.5289	$255.53	$255.55	$255.50
Purchase #2	$206.32	5.479%	$217.6243	$217.62	$217.60	$217.60
Purchase #3	$243.72	12.136%	$273.2979	$273.30	$273.30	$273.30
Purchase #4	$21.39	9.635%	$23.4509	$23.45	$23.45	$23.50
Purchase #5	$83.33	3.789%	$86.4874	$86.49	$86.50	$86.50
Purchase #6	$66.42	9.144%	$72.4934	$72.49	$72.50	$72.50
Purchase #7	$64.28	4.788%	$67.3577	$67.36	$67.35	$67.40
7 purchase totals =	$927.39		$996.2405	$996.24	$996.25	$996.30