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	$139.27	12.368%	$156.4949	$156.49	$156.50	$156.50
Purchase #2	$79.59	5.416%	$83.9006	$83.90	$83.90	$83.90
Purchase #3	$116.32	9.187%	$127.0063	$127.01	$127.00	$127.00
Purchase #4	$42.34	7.260%	$45.4139	$45.41	$45.40	$45.40
Purchase #5	$26.51	4.813%	$27.7859	$27.79	$27.80	$27.80
Purchase #6	$47.42	5.538%	$50.0461	$50.05	$50.05	$50.00
Purchase #7	$144.92	12.531%	$163.0799	$163.08	$163.10	$163.10
7 purchase totals =	$596.37		$653.7276	$653.73	$653.75	$653.70