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	$20.73	12.783%	$23.3799	$23.38	$23.40	$23.40
Purchase #2	$105.72	13.117%	$119.5873	$119.59	$119.60	$119.60
Purchase #3	$74.43	5.424%	$78.4671	$78.47	$78.45	$78.50
Purchase #4	$119.74	3.525%	$123.9608	$123.96	$123.95	$124.00
Purchase #5	$129.34	11.260%	$143.9037	$143.90	$143.90	$143.90
Purchase #6	$242.42	8.454%	$262.9142	$262.91	$262.90	$262.90
Purchase #7	$82.38	3.367%	$85.1537	$85.15	$85.15	$85.20
7 purchase totals =	$774.76		$837.3667	$837.36	$837.35	$837.50