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	$52.59	12.472%	$59.149	$59.15	$59.15	$59.10
Purchase #2	$37.78	11.185%	$42.0057	$42.01	$42.00	$42.00
Purchase #3	$202.42	12.835%	$228.4006	$228.40	$228.40	$228.40
Purchase #4	$43.51	6.125%	$46.175	$46.18	$46.20	$46.20
Purchase #5	$19.85	8.222%	$21.4821	$21.48	$21.50	$21.50
Purchase #6	$234.96	9.203%	$256.5834	$256.58	$256.60	$256.60
Purchase #7	$113.91	8.704%	$123.8247	$123.82	$123.80	$123.80
7 purchase totals =	$705.02		$777.6205	$777.62	$777.65	$777.60