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	$228.80	13.469%	$259.6171	$259.62	$259.60	$259.60
Purchase #2	$119.76	9.577%	$131.2294	$131.23	$131.25	$131.20
Purchase #3	$52.61	3.334%	$54.364	$54.36	$54.35	$54.40
Purchase #4	$100.39	4.594%	$105.0019	$105.00	$105.00	$105.00
Purchase #5	$36.52	11.873%	$40.856	$40.86	$40.85	$40.90
Purchase #6	$140.54	11.551%	$156.7738	$156.77	$156.75	$156.80
Purchase #7	$34.71	9.800%	$38.1116	$38.11	$38.10	$38.10
7 purchase totals =	$713.33		$785.9538	$785.95	$785.90	$786.00