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	$100.57	13.166%	$113.811	$113.81	$113.80	$113.80
Purchase #2	$189.71	6.854%	$202.7127	$202.71	$202.70	$202.70
Purchase #3	$16.50	6.767%	$17.6166	$17.62	$17.60	$17.60
Purchase #4	$180.42	9.129%	$196.8905	$196.89	$196.90	$196.90
Purchase #5	$176.73	13.627%	$200.813	$200.81	$200.80	$200.80
Purchase #6	$106.43	3.232%	$109.8698	$109.87	$109.85	$109.90
Purchase #7	$157.35	5.787%	$166.4558	$166.46	$166.45	$166.50
7 purchase totals =	$927.71		$1,008.1694	$1,008.17	$1,008.10	$1,008.20