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	$239.77	6.333%	$254.9546	$254.95	$254.95	$255.00
Purchase #2	$162.76	3.755%	$168.8716	$168.87	$168.85	$168.90
Purchase #3	$124.66	5.290%	$131.2545	$131.25	$131.25	$131.30
Purchase #4	$155.41	11.567%	$173.3863	$173.39	$173.40	$173.40
Purchase #5	$22.59	12.704%	$25.4598	$25.46	$25.45	$25.50
Purchase #6	$187.82	4.660%	$196.5724	$196.57	$196.55	$196.60
Purchase #7	$197.54	3.144%	$203.7507	$203.75	$203.75	$203.80
7 purchase totals =	$1,090.55		$1,154.2499	$1,154.24	$1,154.20	$1,154.50