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	$8.57	10.427%	$9.4636	$9.46	$9.45	$9.50
Purchase #2	$40.92	4.737%	$42.8584	$42.86	$42.85	$42.90
Purchase #3	$92.92	11.574%	$103.6746	$103.67	$103.65	$103.70
Purchase #4	$100.72	3.511%	$104.2563	$104.26	$104.25	$104.30
Purchase #5	$164.95	12.701%	$185.9003	$185.90	$185.90	$185.90
Purchase #6	$173.81	4.474%	$181.5863	$181.59	$181.60	$181.60
Purchase #7	$181.53	13.794%	$206.5702	$206.57	$206.55	$206.60
7 purchase totals =	$763.42		$834.3097	$834.31	$834.25	$834.50