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	$165.90	11.460%	$184.9121	$184.91	$184.90	$184.90
Purchase #2	$141.36	5.561%	$149.221	$149.22	$149.20	$149.20
Purchase #3	$190.93	9.194%	$208.4841	$208.48	$208.50	$208.50
Purchase #4	$241.45	11.804%	$269.9508	$269.95	$269.95	$270.00
Purchase #5	$115.64	7.116%	$123.8689	$123.87	$123.85	$123.90
Purchase #6	$11.46	10.167%	$12.6251	$12.63	$12.65	$12.60
Purchase #7	$142.73	11.671%	$159.388	$159.39	$159.40	$159.40
7 purchase totals =	$1,009.47		$1,108.4500	$1,108.45	$1,108.45	$1,108.50