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	$231.52	3.403%	$239.3986	$239.40	$239.40	$239.40
Purchase #2	$66.33	5.630%	$70.0644	$70.06	$70.05	$70.10
Purchase #3	$196.46	13.210%	$222.4124	$222.41	$222.40	$222.40
Purchase #4	$65.41	12.722%	$73.7315	$73.73	$73.75	$73.70
Purchase #5	$99.84	6.648%	$106.4774	$106.48	$106.50	$106.50
Purchase #6	$52.84	11.621%	$58.9805	$58.98	$59.00	$59.00
Purchase #7	$69.94	12.138%	$78.4293	$78.43	$78.45	$78.40
7 purchase totals =	$782.34		$849.4941	$849.49	$849.55	$849.50