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	12.540%	$280.5285	$280.53	$280.55	$280.50
Purchase #2	$155.27	6.409%	$165.2213	$165.22	$165.20	$165.20
Purchase #3	$119.46	4.414%	$124.733	$124.73	$124.75	$124.70
Purchase #4	$40.37	11.102%	$44.8519	$44.85	$44.85	$44.90
Purchase #5	$196.59	11.432%	$219.0642	$219.06	$219.05	$219.10
Purchase #6	$230.80	12.361%	$259.3292	$259.33	$259.35	$259.30
Purchase #7	$57.78	3.461%	$59.7798	$59.78	$59.80	$59.80
7 purchase totals =	$1,049.54		$1,153.5079	$1,153.50	$1,153.55	$1,153.50