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	$104.91	10.649%	$116.0819	$116.08	$116.10	$116.10
Purchase #2	$54.73	8.592%	$59.4324	$59.43	$59.45	$59.40
Purchase #3	$62.90	9.230%	$68.7057	$68.71	$68.70	$68.70
Purchase #4	$76.46	9.413%	$83.6572	$83.66	$83.65	$83.70
Purchase #5	$63.50	3.757%	$65.8857	$65.89	$65.90	$65.90
Purchase #6	$120.72	3.659%	$125.1371	$125.14	$125.15	$125.10
Purchase #7	$139.65	5.684%	$147.5877	$147.59	$147.60	$147.60
7 purchase totals =	$622.87		$666.4877	$666.50	$666.55	$666.50