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	$205.34	9.791%	$225.4448	$225.44	$225.45	$225.40
Purchase #2	$31.47	12.142%	$35.2911	$35.29	$35.30	$35.30
Purchase #3	$174.85	4.518%	$182.7497	$182.75	$182.75	$182.70
Purchase #4	$180.50	10.565%	$199.5698	$199.57	$199.55	$199.60
Purchase #5	$132.82	4.756%	$139.1369	$139.14	$139.15	$139.10
Purchase #6	$204.78	5.273%	$215.578	$215.58	$215.60	$215.60
Purchase #7	$232.55	11.194%	$258.5816	$258.58	$258.60	$258.60
7 purchase totals =	$1,162.31		$1,256.3519	$1,256.35	$1,256.40	$1,256.30