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	$48.41	5.182%	$50.9186	$50.92	$50.90	$50.90
Purchase #2	$35.61	6.247%	$37.8346	$37.83	$37.85	$37.80
Purchase #3	$58.97	12.678%	$66.4462	$66.45	$66.45	$66.40
Purchase #4	$187.64	12.328%	$210.7723	$210.77	$210.75	$210.80
Purchase #5	$93.27	10.481%	$103.0456	$103.05	$103.05	$103.00
Purchase #6	$147.90	6.833%	$158.006	$158.01	$158.00	$158.00
Purchase #7	$35.78	12.315%	$40.1863	$40.19	$40.20	$40.20
7 purchase totals =	$607.58		$667.2096	$667.22	$667.20	$667.10