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	$127.30	9.587%	$139.5043	$139.50	$139.50	$139.50
Purchase #2	$245.39	7.636%	$264.128	$264.13	$264.15	$264.10
Purchase #3	$146.71	8.237%	$158.7945	$158.79	$158.80	$158.80
Purchase #4	$50.81	9.657%	$55.7167	$55.72	$55.70	$55.70
Purchase #5	$194.49	5.640%	$205.4592	$205.46	$205.45	$205.50
Purchase #6	$168.88	7.801%	$182.0543	$182.05	$182.05	$182.10
Purchase #7	$30.67	4.138%	$31.9391	$31.94	$31.95	$31.90
7 purchase totals =	$964.25		$1,037.5961	$1,037.59	$1,037.60	$1,037.60