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	$83.79	5.658%	$88.5308	$88.53	$88.55	$88.50
Purchase #2	$98.64	6.348%	$104.9017	$104.90	$104.90	$104.90
Purchase #3	$27.77	12.573%	$31.2615	$31.26	$31.25	$31.30
Purchase #4	$76.75	7.404%	$82.4326	$82.43	$82.45	$82.40
Purchase #5	$135.59	12.529%	$152.5781	$152.58	$152.60	$152.60
Purchase #6	$21.78	7.292%	$23.3682	$23.37	$23.35	$23.40
Purchase #7	$18.68	9.607%	$20.4746	$20.47	$20.45	$20.50
7 purchase totals =	$463.00		$503.5475	$503.54	$503.55	$503.60