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	$205.27	11.788%	$229.4672	$229.47	$229.45	$229.50
Purchase #2	$133.29	8.311%	$144.3677	$144.37	$144.35	$144.40
Purchase #3	$107.81	10.429%	$119.0535	$119.05	$119.05	$119.10
Purchase #4	$165.67	6.591%	$176.5893	$176.59	$176.60	$176.60
Purchase #5	$171.91	7.834%	$185.3774	$185.38	$185.40	$185.40
Purchase #6	$71.33	10.378%	$78.7326	$78.73	$78.75	$78.70
Purchase #7	$96.40	10.535%	$106.5557	$106.56	$106.55	$106.60
7 purchase totals =	$951.68		$1,040.1434	$1,040.15	$1,040.15	$1,040.30