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	$70.89	9.226%	$77.4303	$77.43	$77.45	$77.40
Purchase #2	$141.67	11.860%	$158.4721	$158.47	$158.45	$158.50
Purchase #3	$188.66	5.410%	$198.8665	$198.87	$198.85	$198.90
Purchase #4	$116.57	4.626%	$121.9625	$121.96	$121.95	$122.00
Purchase #5	$243.39	3.228%	$251.2466	$251.25	$251.25	$251.20
Purchase #6	$244.64	4.432%	$255.4824	$255.48	$255.50	$255.50
Purchase #7	$105.96	10.325%	$116.9004	$116.90	$116.90	$116.90
7 purchase totals =	$1,111.78		$1,180.3608	$1,180.36	$1,180.35	$1,180.40