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	$37.88	6.627%	$40.3903	$40.39	$40.40	$40.40
Purchase #2	$30.25	6.105%	$32.0968	$32.10	$32.10	$32.10
Purchase #3	$231.98	7.542%	$249.4759	$249.48	$249.50	$249.50
Purchase #4	$140.74	8.523%	$152.7353	$152.74	$152.75	$152.70
Purchase #5	$74.55	6.761%	$79.5903	$79.59	$79.60	$79.60
Purchase #6	$245.76	3.781%	$255.0522	$255.05	$255.05	$255.10
Purchase #7	$26.85	3.807%	$27.8722	$27.87	$27.85	$27.90
7 purchase totals =	$788.01		$837.2130	$837.22	$837.25	$837.30