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	$105.33	12.703%	$118.7101	$118.71	$118.70	$118.70
Purchase #2	$40.49	13.403%	$45.9169	$45.92	$45.90	$45.90
Purchase #3	$54.75	8.679%	$59.5018	$59.50	$59.50	$59.50
Purchase #4	$153.50	3.284%	$158.5409	$158.54	$158.55	$158.50
Purchase #5	$229.75	8.803%	$249.9749	$249.97	$249.95	$250.00
Purchase #6	$183.76	10.695%	$203.4131	$203.41	$203.40	$203.40
Purchase #7	$217.90	13.106%	$246.458	$246.46	$246.45	$246.50
7 purchase totals =	$985.48		$1,082.5157	$1,082.51	$1,082.45	$1,082.50