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	$226.33	11.293%	$251.8894	$251.89	$251.90	$251.90
Purchase #2	$166.34	3.770%	$172.611	$172.61	$172.60	$172.60
Purchase #3	$115.90	6.459%	$123.386	$123.39	$123.40	$123.40
Purchase #4	$18.34	11.646%	$20.4759	$20.48	$20.50	$20.50
Purchase #5	$137.80	9.704%	$151.1721	$151.17	$151.15	$151.20
Purchase #6	$99.72	4.284%	$103.992	$103.99	$104.00	$104.00
Purchase #7	$141.79	4.846%	$148.6611	$148.66	$148.65	$148.70
7 purchase totals =	$906.22		$972.1875	$972.19	$972.20	$972.30