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	$152.90	5.226%	$160.8906	$160.89	$160.90	$160.90
Purchase #2	$246.69	4.756%	$258.4226	$258.42	$258.40	$258.40
Purchase #3	$137.25	3.670%	$142.2871	$142.29	$142.30	$142.30
Purchase #4	$224.39	11.414%	$250.0019	$250.00	$250.00	$250.00
Purchase #5	$85.76	12.633%	$96.5941	$96.59	$96.60	$96.60
Purchase #6	$133.81	9.442%	$146.4443	$146.44	$146.45	$146.40
Purchase #7	$225.28	3.854%	$233.9623	$233.96	$233.95	$234.00
7 purchase totals =	$1,206.08		$1,288.6029	$1,288.59	$1,288.60	$1,288.60