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	$60.31	11.218%	$67.0756	$67.08	$67.10	$67.10
Purchase #2	$49.66	11.682%	$55.4613	$55.46	$55.45	$55.50
Purchase #3	$219.97	5.209%	$231.4282	$231.43	$231.45	$231.40
Purchase #4	$52.57	4.432%	$54.8999	$54.90	$54.90	$54.90
Purchase #5	$149.53	3.354%	$154.5452	$154.55	$154.55	$154.50
Purchase #6	$168.57	4.180%	$175.6162	$175.62	$175.60	$175.60
Purchase #7	$47.47	6.376%	$50.4967	$50.50	$50.50	$50.50
7 purchase totals =	$748.08		$789.5231	$789.54	$789.55	$789.50