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	$231.74	10.175%	$255.3195	$255.32	$255.30	$255.30
Purchase #2	$242.37	5.679%	$256.1342	$256.13	$256.15	$256.10
Purchase #3	$13.90	12.507%	$15.6385	$15.64	$15.65	$15.60
Purchase #4	$216.77	7.371%	$232.7481	$232.75	$232.75	$232.70
Purchase #5	$160.83	12.152%	$180.3741	$180.37	$180.35	$180.40
Purchase #6	$119.25	11.380%	$132.8207	$132.82	$132.80	$132.80
Purchase #7	$90.74	6.818%	$96.9267	$96.93	$96.95	$96.90
7 purchase totals =	$1,075.60		$1,169.9618	$1,169.96	$1,169.95	$1,169.80