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	$113.77	11.844%	$127.2449	$127.24	$127.25	$127.20
Purchase #2	$192.77	9.443%	$210.9733	$210.97	$210.95	$211.00
Purchase #3	$74.81	10.266%	$82.49	$82.49	$82.50	$82.50
Purchase #4	$42.81	4.589%	$44.7746	$44.77	$44.75	$44.80
Purchase #5	$209.25	8.225%	$226.4608	$226.46	$226.45	$226.50
Purchase #6	$236.79	11.693%	$264.4779	$264.48	$264.50	$264.50
Purchase #7	$35.89	3.119%	$37.0094	$37.01	$37.00	$37.00
7 purchase totals =	$906.09		$993.4309	$993.42	$993.40	$993.50