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	$111.64	10.581%	$123.4526	$123.45	$123.45	$123.50
Purchase #2	$126.94	12.406%	$142.6882	$142.69	$142.70	$142.70
Purchase #3	$130.82	6.581%	$139.4293	$139.43	$139.45	$139.40
Purchase #4	$239.67	6.673%	$255.6632	$255.66	$255.65	$255.70
Purchase #5	$67.51	9.518%	$73.9356	$73.94	$73.95	$73.90
Purchase #6	$136.59	13.508%	$155.0406	$155.04	$155.05	$155.00
Purchase #7	$136.99	9.677%	$150.2465	$150.25	$150.25	$150.20
7 purchase totals =	$950.16		$1,040.4560	$1,040.46	$1,040.50	$1,040.40