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	$189.63	12.822%	$213.9444	$213.94	$213.95	$213.90
Purchase #2	$65.65	9.341%	$71.7824	$71.78	$71.80	$71.80
Purchase #3	$102.39	9.504%	$112.1211	$112.12	$112.10	$112.10
Purchase #4	$75.51	4.444%	$78.8657	$78.87	$78.85	$78.90
Purchase #5	$56.62	7.619%	$60.9339	$60.93	$60.95	$60.90
Purchase #6	$49.88	4.309%	$52.0293	$52.03	$52.05	$52.00
Purchase #7	$242.51	4.455%	$253.3138	$253.31	$253.30	$253.30
7 purchase totals =	$782.19		$842.9906	$842.98	$843.00	$842.90