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	$129.99	10.380%	$143.483	$143.48	$143.50	$143.50
Purchase #2	$73.26	9.300%	$80.0732	$80.07	$80.05	$80.10
Purchase #3	$74.64	5.170%	$78.4989	$78.50	$78.50	$78.50
Purchase #4	$143.82	10.767%	$159.3051	$159.31	$159.30	$159.30
Purchase #5	$6.94	13.178%	$7.8546	$7.85	$7.85	$7.90
Purchase #6	$46.79	10.140%	$51.5345	$51.53	$51.55	$51.50
Purchase #7	$37.78	3.223%	$38.9976	$39.00	$39.00	$39.00
7 purchase totals =	$513.22		$559.7469	$559.74	$559.75	$559.80