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	$115.73	13.619%	$131.4913	$131.49	$131.50	$131.50
Purchase #2	$84.33	10.448%	$93.1408	$93.14	$93.15	$93.10
Purchase #3	$186.97	10.102%	$205.8577	$205.86	$205.85	$205.90
Purchase #4	$108.89	13.505%	$123.5956	$123.60	$123.60	$123.60
Purchase #5	$21.85	7.775%	$23.5488	$23.55	$23.55	$23.50
Purchase #6	$100.37	13.788%	$114.209	$114.21	$114.20	$114.20
Purchase #7	$26.64	6.830%	$28.4595	$28.46	$28.45	$28.50
7 purchase totals =	$644.78		$720.3027	$720.31	$720.30	$720.30