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	$247.73	12.593%	$278.9266	$278.93	$278.95	$278.90
Purchase #2	$86.55	4.600%	$90.5313	$90.53	$90.55	$90.50
Purchase #3	$139.47	6.224%	$148.1506	$148.15	$148.15	$148.20
Purchase #4	$95.55	12.345%	$107.3456	$107.35	$107.35	$107.30
Purchase #5	$200.86	4.833%	$210.5676	$210.57	$210.55	$210.60
Purchase #6	$197.48	8.558%	$214.3803	$214.38	$214.40	$214.40
Purchase #7	$50.96	7.854%	$54.9624	$54.96	$54.95	$55.00
7 purchase totals =	$1,018.60		$1,104.8644	$1,104.87	$1,104.90	$1,104.90