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	$115.93	12.413%	$130.3204	$130.32	$130.30	$130.30
Purchase #2	$117.96	13.202%	$133.5331	$133.53	$133.55	$133.50
Purchase #3	$93.48	7.211%	$100.2208	$100.22	$100.20	$100.20
Purchase #4	$36.94	10.798%	$40.9288	$40.93	$40.95	$40.90
Purchase #5	$139.90	11.353%	$155.7828	$155.78	$155.80	$155.80
Purchase #6	$142.87	9.526%	$156.4798	$156.48	$156.50	$156.50
Purchase #7	$19.90	8.218%	$21.5354	$21.54	$21.55	$21.50
7 purchase totals =	$666.98		$738.8011	$738.80	$738.85	$738.70