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	$117.93	4.331%	$123.0375	$123.04	$123.05	$123.00
Purchase #2	$133.51	8.545%	$144.9184	$144.92	$144.90	$144.90
Purchase #3	$27.89	9.342%	$30.4955	$30.50	$30.50	$30.50
Purchase #4	$149.84	3.488%	$155.0664	$155.07	$155.05	$155.10
Purchase #5	$82.89	4.304%	$86.4576	$86.46	$86.45	$86.50
Purchase #6	$132.95	7.342%	$142.7112	$142.71	$142.70	$142.70
Purchase #7	$148.38	10.630%	$164.1528	$164.15	$164.15	$164.20
7 purchase totals =	$793.39		$846.8394	$846.85	$846.80	$846.90