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	$62.70	13.256%	$71.0115	$71.01	$71.00	$71.00
Purchase #2	$116.86	4.393%	$121.9937	$121.99	$122.00	$122.00
Purchase #3	$189.25	3.640%	$196.1387	$196.14	$196.15	$196.10
Purchase #4	$49.83	10.164%	$54.8947	$54.89	$54.90	$54.90
Purchase #5	$227.79	12.219%	$255.6237	$255.62	$255.60	$255.60
Purchase #6	$56.97	4.283%	$59.41	$59.41	$59.40	$59.40
Purchase #7	$116.54	12.304%	$130.8791	$130.88	$130.90	$130.90
7 purchase totals =	$819.94		$889.9514	$889.94	$889.95	$889.90