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	$145.63	13.614%	$165.4561	$165.46	$165.45	$165.50
Purchase #2	$116.44	6.409%	$123.9026	$123.90	$123.90	$123.90
Purchase #3	$123.68	11.530%	$137.9403	$137.94	$137.95	$137.90
Purchase #4	$140.54	10.675%	$155.5426	$155.54	$155.55	$155.50
Purchase #5	$104.64	13.693%	$118.9684	$118.97	$118.95	$119.00
Purchase #6	$52.89	8.424%	$57.3455	$57.35	$57.35	$57.30
Purchase #7	$150.88	3.770%	$156.5682	$156.57	$156.55	$156.60
7 purchase totals =	$834.70		$915.7237	$915.73	$915.70	$915.70