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	$92.37	8.698%	$100.4043	$100.40	$100.40	$100.40
Purchase #2	$51.59	13.439%	$58.5232	$58.52	$58.50	$58.50
Purchase #3	$210.27	7.732%	$226.5281	$226.53	$226.55	$226.50
Purchase #4	$130.89	8.153%	$141.5615	$141.56	$141.55	$141.60
Purchase #5	$207.35	10.636%	$229.4037	$229.40	$229.40	$229.40
Purchase #6	$180.30	13.269%	$204.224	$204.22	$204.20	$204.20
Purchase #7	$70.59	13.751%	$80.2968	$80.30	$80.30	$80.30
7 purchase totals =	$943.36		$1,040.9416	$1,040.93	$1,040.90	$1,040.90