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	$139.78	3.356%	$144.471	$144.47	$144.45	$144.50
Purchase #2	$120.96	3.102%	$124.7122	$124.71	$124.70	$124.70
Purchase #3	$40.66	3.856%	$42.2278	$42.23	$42.25	$42.20
Purchase #4	$51.26	5.792%	$54.229	$54.23	$54.25	$54.20
Purchase #5	$129.25	11.422%	$144.0129	$144.01	$144.00	$144.00
Purchase #6	$89.43	4.478%	$93.4347	$93.43	$93.45	$93.40
Purchase #7	$30.31	7.183%	$32.4872	$32.49	$32.50	$32.50
7 purchase totals =	$601.65		$635.5748	$635.57	$635.60	$635.50