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	$27.64	13.155%	$31.276	$31.28	$31.30	$31.30
Purchase #2	$43.59	8.577%	$47.3287	$47.33	$47.35	$47.30
Purchase #3	$216.41	4.398%	$225.9277	$225.93	$225.95	$225.90
Purchase #4	$89.67	12.187%	$100.5981	$100.60	$100.60	$100.60
Purchase #5	$89.26	10.297%	$98.4511	$98.45	$98.45	$98.50
Purchase #6	$160.69	13.543%	$182.4522	$182.45	$182.45	$182.50
Purchase #7	$214.50	7.762%	$231.1495	$231.15	$231.15	$231.10
7 purchase totals =	$841.76		$917.1833	$917.19	$917.25	$917.20