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	$14.69	11.850%	$16.4308	$16.43	$16.45	$16.40
Purchase #2	$138.51	6.434%	$147.4217	$147.42	$147.40	$147.40
Purchase #3	$147.88	3.351%	$152.8355	$152.84	$152.85	$152.80
Purchase #4	$54.80	7.829%	$59.0903	$59.09	$59.10	$59.10
Purchase #5	$240.57	3.873%	$249.8873	$249.89	$249.90	$249.90
Purchase #6	$240.67	6.649%	$256.6721	$256.67	$256.65	$256.70
Purchase #7	$193.65	7.675%	$208.5126	$208.51	$208.50	$208.50
7 purchase totals =	$1,030.77		$1,090.8503	$1,090.85	$1,090.85	$1,090.80