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	$249.27	12.459%	$280.3265	$280.33	$280.35	$280.30
Purchase #2	$156.97	11.811%	$175.5097	$175.51	$175.50	$175.50
Purchase #3	$122.89	6.662%	$131.0769	$131.08	$131.10	$131.10
Purchase #4	$212.69	6.800%	$227.1529	$227.15	$227.15	$227.20
Purchase #5	$54.77	8.708%	$59.5394	$59.54	$59.55	$59.50
Purchase #6	$105.45	13.260%	$119.4327	$119.43	$119.45	$119.40
Purchase #7	$87.92	5.155%	$92.4523	$92.45	$92.45	$92.50
7 purchase totals =	$989.96		$1,085.4904	$1,085.49	$1,085.55	$1,085.50