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	$139.40	5.606%	$147.2148	$147.21	$147.20	$147.20
Purchase #2	$234.91	12.815%	$265.0137	$265.01	$265.00	$265.00
Purchase #3	$217.31	6.511%	$231.4591	$231.46	$231.45	$231.50
Purchase #4	$57.77	13.542%	$65.5932	$65.59	$65.60	$65.60
Purchase #5	$183.57	13.533%	$208.4125	$208.41	$208.40	$208.40
Purchase #6	$29.44	11.311%	$32.77	$32.77	$32.75	$32.80
Purchase #7	$65.86	9.452%	$72.0851	$72.09	$72.10	$72.10
7 purchase totals =	$928.26		$1,022.5484	$1,022.54	$1,022.50	$1,022.60