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	$25.77	4.392%	$26.9018	$26.90	$26.90	$26.90
Purchase #2	$190.95	7.503%	$205.277	$205.28	$205.30	$205.30
Purchase #3	$245.69	4.564%	$256.9033	$256.90	$256.90	$256.90
Purchase #4	$179.71	5.273%	$189.1861	$189.19	$189.20	$189.20
Purchase #5	$65.33	3.345%	$67.5153	$67.52	$67.50	$67.50
Purchase #6	$119.73	11.156%	$133.0871	$133.09	$133.10	$133.10
Purchase #7	$50.72	7.585%	$54.5671	$54.57	$54.55	$54.60
7 purchase totals =	$877.90		$933.4377	$933.45	$933.45	$933.50