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	$183.48	11.417%	$204.4279	$204.43	$204.45	$204.40
Purchase #2	$124.65	7.670%	$134.2107	$134.21	$134.20	$134.20
Purchase #3	$133.98	13.196%	$151.66	$151.66	$151.65	$151.70
Purchase #4	$37.71	5.785%	$39.8915	$39.89	$39.90	$39.90
Purchase #5	$70.43	9.122%	$76.8546	$76.85	$76.85	$76.90
Purchase #6	$90.26	11.265%	$100.4278	$100.43	$100.45	$100.40
Purchase #7	$245.96	13.850%	$280.0255	$280.03	$280.05	$280.00
7 purchase totals =	$886.47		$987.4980	$987.50	$987.55	$987.50