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	$82.25	7.449%	$88.3768	$88.38	$88.40	$88.40
Purchase #2	$39.86	3.792%	$41.3715	$41.37	$41.35	$41.40
Purchase #3	$145.75	12.378%	$163.7909	$163.79	$163.80	$163.80
Purchase #4	$104.47	4.677%	$109.3561	$109.36	$109.35	$109.40
Purchase #5	$72.27	4.589%	$75.5865	$75.59	$75.60	$75.60
Purchase #6	$106.37	4.436%	$111.0886	$111.09	$111.10	$111.10
Purchase #7	$77.59	10.721%	$85.9084	$85.91	$85.90	$85.90
7 purchase totals =	$628.56		$675.4788	$675.49	$675.50	$675.60