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	$13.59	3.804%	$14.107	$14.11	$14.10	$14.10
Purchase #2	$141.99	7.380%	$152.4689	$152.47	$152.45	$152.50
Purchase #3	$119.68	4.384%	$124.9268	$124.93	$124.95	$124.90
Purchase #4	$20.45	6.685%	$21.8171	$21.82	$21.80	$21.80
Purchase #5	$164.80	12.724%	$185.7692	$185.77	$185.75	$185.80
Purchase #6	$65.25	7.708%	$70.2795	$70.28	$70.30	$70.30
Purchase #7	$184.49	8.850%	$200.8174	$200.82	$200.80	$200.80
7 purchase totals =	$710.25		$770.1859	$770.20	$770.15	$770.20