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	$59.69	11.766%	$66.7131	$66.71	$66.70	$66.70
Purchase #2	$82.47	8.185%	$89.2202	$89.22	$89.20	$89.20
Purchase #3	$148.98	7.728%	$160.4932	$160.49	$160.50	$160.50
Purchase #4	$62.96	4.440%	$65.7554	$65.76	$65.75	$65.80
Purchase #5	$79.46	5.136%	$83.5411	$83.54	$83.55	$83.50
Purchase #6	$119.93	12.335%	$134.7234	$134.72	$134.70	$134.70
Purchase #7	$71.82	7.517%	$77.2187	$77.22	$77.20	$77.20
7 purchase totals =	$625.31		$677.6651	$677.66	$677.60	$677.60