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	$51.56	6.624%	$54.9753	$54.98	$55.00	$55.00
Purchase #2	$211.28	13.858%	$240.5592	$240.56	$240.55	$240.60
Purchase #3	$104.36	10.186%	$114.9901	$114.99	$115.00	$115.00
Purchase #4	$54.28	9.470%	$59.4203	$59.42	$59.40	$59.40
Purchase #5	$144.77	11.580%	$161.5344	$161.53	$161.55	$161.50
Purchase #6	$76.70	12.851%	$86.5567	$86.56	$86.55	$86.60
Purchase #7	$39.33	10.309%	$43.3845	$43.38	$43.40	$43.40
7 purchase totals =	$682.28		$761.4205	$761.42	$761.45	$761.50