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	$246.50	4.314%	$257.134	$257.13	$257.15	$257.10
Purchase #2	$143.77	3.175%	$148.3347	$148.33	$148.35	$148.30
Purchase #3	$48.87	6.440%	$52.0172	$52.02	$52.00	$52.00
Purchase #4	$89.26	12.417%	$100.3434	$100.34	$100.35	$100.30
Purchase #5	$161.56	13.513%	$183.3916	$183.39	$183.40	$183.40
Purchase #6	$121.72	9.692%	$133.5171	$133.52	$133.50	$133.50
Purchase #7	$28.85	10.198%	$31.7921	$31.79	$31.80	$31.80
7 purchase totals =	$840.53		$906.5301	$906.52	$906.55	$906.40