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	$141.30	13.440%	$160.2907	$160.29	$160.30	$160.30
Purchase #2	$66.29	13.795%	$75.4347	$75.43	$75.45	$75.40
Purchase #3	$15.94	6.405%	$16.961	$16.96	$16.95	$17.00
Purchase #4	$43.76	4.825%	$45.8714	$45.87	$45.85	$45.90
Purchase #5	$50.82	11.481%	$56.6546	$56.65	$56.65	$56.70
Purchase #6	$99.82	9.453%	$109.256	$109.26	$109.25	$109.30
Purchase #7	$210.87	6.139%	$223.8153	$223.82	$223.80	$223.80
7 purchase totals =	$628.80		$688.2837	$688.28	$688.25	$688.40