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	$51.35	5.175%	$54.0074	$54.01	$54.00	$54.00
Purchase #2	$73.42	6.447%	$78.1534	$78.15	$78.15	$78.20
Purchase #3	$99.83	13.115%	$112.9227	$112.92	$112.90	$112.90
Purchase #4	$194.25	9.541%	$212.7834	$212.78	$212.80	$212.80
Purchase #5	$89.29	3.787%	$92.6714	$92.67	$92.65	$92.70
Purchase #6	$82.72	13.242%	$93.6738	$93.67	$93.65	$93.70
Purchase #7	$229.25	12.618%	$258.1768	$258.18	$258.20	$258.20
7 purchase totals =	$820.11		$902.3889	$902.38	$902.35	$902.50