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	$19.43	12.825%	$21.9219	$21.92	$21.90	$21.90
Purchase #2	$246.67	4.833%	$258.5916	$258.59	$258.60	$258.60
Purchase #3	$86.94	3.236%	$89.7534	$89.75	$89.75	$89.80
Purchase #4	$217.46	4.832%	$227.9677	$227.97	$227.95	$228.00
Purchase #5	$213.63	5.557%	$225.5014	$225.50	$225.50	$225.50
Purchase #6	$115.93	6.782%	$123.7924	$123.79	$123.80	$123.80
Purchase #7	$166.60	11.409%	$185.6074	$185.61	$185.60	$185.60
7 purchase totals =	$1,066.66		$1,133.1358	$1,133.13	$1,133.10	$1,133.20