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	$223.35	12.773%	$251.8785	$251.88	$251.90	$251.90
Purchase #2	$104.50	9.277%	$114.1945	$114.19	$114.20	$114.20
Purchase #3	$132.68	5.217%	$139.6019	$139.60	$139.60	$139.60
Purchase #4	$206.35	13.299%	$233.7925	$233.79	$233.80	$233.80
Purchase #5	$56.54	4.529%	$59.1007	$59.10	$59.10	$59.10
Purchase #6	$179.75	4.265%	$187.4163	$187.42	$187.40	$187.40
Purchase #7	$74.64	7.862%	$80.5082	$80.51	$80.50	$80.50
7 purchase totals =	$977.81		$1,066.4926	$1,066.49	$1,066.50	$1,066.50