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	$231.93	10.190%	$255.5637	$255.56	$255.55	$255.60
Purchase #2	$56.86	10.445%	$62.799	$62.80	$62.80	$62.80
Purchase #3	$129.73	9.820%	$142.4695	$142.47	$142.45	$142.50
Purchase #4	$138.48	12.512%	$155.8066	$155.81	$155.80	$155.80
Purchase #5	$211.30	12.166%	$237.0068	$237.01	$237.00	$237.00
Purchase #6	$83.28	4.180%	$86.7611	$86.76	$86.75	$86.80
Purchase #7	$77.52	13.270%	$87.8069	$87.81	$87.80	$87.80
7 purchase totals =	$929.10		$1,028.2136	$1,028.22	$1,028.15	$1,028.30