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	$50.65	11.508%	$56.4788	$56.48	$56.50	$56.50
Purchase #2	$218.47	9.372%	$238.945	$238.95	$238.95	$238.90
Purchase #3	$181.38	5.412%	$191.1963	$191.20	$191.20	$191.20
Purchase #4	$136.82	6.815%	$146.1443	$146.14	$146.15	$146.10
Purchase #5	$17.99	11.220%	$20.0085	$20.01	$20.00	$20.00
Purchase #6	$121.48	5.858%	$128.5963	$128.60	$128.60	$128.60
Purchase #7	$180.34	11.142%	$200.4335	$200.43	$200.45	$200.40
7 purchase totals =	$907.13		$981.8027	$981.81	$981.85	$981.70