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	$65.55	3.421%	$67.7925	$67.79	$67.80	$67.80
Purchase #2	$229.86	13.333%	$260.5072	$260.51	$260.50	$260.50
Purchase #3	$80.27	3.174%	$82.8178	$82.82	$82.80	$82.80
Purchase #4	$198.84	13.575%	$225.8325	$225.83	$225.85	$225.80
Purchase #5	$78.69	5.263%	$82.8315	$82.83	$82.85	$82.80
Purchase #6	$142.95	7.412%	$153.5455	$153.55	$153.55	$153.50
Purchase #7	$18.81	13.643%	$21.3762	$21.38	$21.40	$21.40
7 purchase totals =	$814.97		$894.7032	$894.71	$894.75	$894.60