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	$201.61	11.834%	$225.4685	$225.47	$225.45	$225.50
Purchase #2	$222.33	9.205%	$242.7955	$242.80	$242.80	$242.80
Purchase #3	$173.43	5.857%	$183.5878	$183.59	$183.60	$183.60
Purchase #4	$31.60	5.419%	$33.3124	$33.31	$33.30	$33.30
Purchase #5	$11.61	10.238%	$12.7986	$12.80	$12.80	$12.80
Purchase #6	$131.55	10.573%	$145.4588	$145.46	$145.45	$145.50
Purchase #7	$237.30	8.428%	$257.2996	$257.30	$257.30	$257.30
7 purchase totals =	$1,009.43		$1,100.7212	$1,100.73	$1,100.70	$1,100.80