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	$53.45	9.663%	$58.6149	$58.61	$58.60	$58.60
Purchase #2	$97.69	13.584%	$110.9602	$110.96	$110.95	$111.00
Purchase #3	$237.33	6.654%	$253.1219	$253.12	$253.10	$253.10
Purchase #4	$140.89	3.799%	$146.2424	$146.24	$146.25	$146.20
Purchase #5	$102.70	8.505%	$111.4346	$111.43	$111.45	$111.40
Purchase #6	$59.86	5.268%	$63.0134	$63.01	$63.00	$63.00
Purchase #7	$223.63	6.189%	$237.4705	$237.47	$237.45	$237.50
7 purchase totals =	$915.55		$980.8579	$980.84	$980.80	$980.80