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	$84.33	6.633%	$89.9236	$89.92	$89.90	$89.90
Purchase #2	$225.33	13.857%	$256.554	$256.55	$256.55	$256.60
Purchase #3	$162.35	12.517%	$182.6713	$182.67	$182.65	$182.70
Purchase #4	$105.88	12.181%	$118.7772	$118.78	$118.80	$118.80
Purchase #5	$151.44	11.452%	$168.7829	$168.78	$168.80	$168.80
Purchase #6	$226.53	8.864%	$246.6096	$246.61	$246.60	$246.60
Purchase #7	$240.30	10.389%	$265.2648	$265.26	$265.25	$265.30
7 purchase totals =	$1,196.16		$1,328.5834	$1,328.57	$1,328.55	$1,328.70