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	$167.91	11.654%	$187.4782	$187.48	$187.50	$187.50
Purchase #2	$187.51	9.673%	$205.6478	$205.65	$205.65	$205.60
Purchase #3	$20.67	7.801%	$22.2825	$22.28	$22.30	$22.30
Purchase #4	$170.80	4.565%	$178.597	$178.60	$178.60	$178.60
Purchase #5	$37.32	12.800%	$42.097	$42.10	$42.10	$42.10
Purchase #6	$44.78	13.664%	$50.8987	$50.90	$50.90	$50.90
Purchase #7	$204.38	13.367%	$231.6995	$231.70	$231.70	$231.70
7 purchase totals =	$833.37		$918.7007	$918.71	$918.75	$918.70