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	$60.42	3.485%	$62.5256	$62.53	$62.55	$62.50
Purchase #2	$213.76	12.500%	$240.48	$240.48	$240.50	$240.50
Purchase #3	$155.70	7.819%	$167.8742	$167.87	$167.85	$167.90
Purchase #4	$94.47	6.391%	$100.5076	$100.51	$100.50	$100.50
Purchase #5	$35.37	12.717%	$39.868	$39.87	$39.85	$39.90
Purchase #6	$64.63	5.716%	$68.3243	$68.32	$68.30	$68.30
Purchase #7	$245.77	3.866%	$255.2715	$255.27	$255.25	$255.30
7 purchase totals =	$870.12		$934.8512	$934.85	$934.80	$934.90