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	$234.26	9.611%	$256.7747	$256.77	$256.75	$256.80
Purchase #2	$87.65	3.227%	$90.4785	$90.48	$90.50	$90.50
Purchase #3	$84.37	5.565%	$89.0652	$89.07	$89.05	$89.10
Purchase #4	$213.32	13.732%	$242.6131	$242.61	$242.60	$242.60
Purchase #5	$18.87	11.106%	$20.9657	$20.97	$20.95	$21.00
Purchase #6	$151.45	13.127%	$171.3308	$171.33	$171.35	$171.30
Purchase #7	$232.86	10.840%	$258.102	$258.10	$258.10	$258.10
7 purchase totals =	$1,022.78		$1,129.3300	$1,129.33	$1,129.30	$1,129.40