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	$86.42	3.132%	$89.1267	$89.13	$89.15	$89.10
Purchase #2	$244.82	8.646%	$265.9871	$265.99	$266.00	$266.00
Purchase #3	$179.54	4.260%	$187.1884	$187.19	$187.20	$187.20
Purchase #4	$32.90	6.536%	$35.0503	$35.05	$35.05	$35.10
Purchase #5	$233.52	8.508%	$253.3879	$253.39	$253.40	$253.40
Purchase #6	$140.54	12.777%	$158.4968	$158.50	$158.50	$158.50
Purchase #7	$21.72	8.216%	$23.5045	$23.50	$23.50	$23.50
7 purchase totals =	$939.46		$1,012.7417	$1,012.75	$1,012.80	$1,012.80