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	$55.85	4.520%	$58.3744	$58.37	$58.35	$58.40
Purchase #2	$54.78	7.274%	$58.7647	$58.76	$58.75	$58.80
Purchase #3	$194.60	11.423%	$216.8292	$216.83	$216.85	$216.80
Purchase #4	$165.65	9.153%	$180.8119	$180.81	$180.80	$180.80
Purchase #5	$91.82	12.266%	$103.0826	$103.08	$103.10	$103.10
Purchase #6	$48.32	8.262%	$52.3122	$52.31	$52.30	$52.30
Purchase #7	$65.57	9.471%	$71.7801	$71.78	$71.80	$71.80
7 purchase totals =	$676.59		$741.9551	$741.94	$741.95	$742.00