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	$132.91	3.398%	$137.4263	$137.43	$137.45	$137.40
Purchase #2	$233.88	3.168%	$241.2893	$241.29	$241.30	$241.30
Purchase #3	$120.80	9.633%	$132.4367	$132.44	$132.45	$132.40
Purchase #4	$23.30	9.814%	$25.5867	$25.59	$25.60	$25.60
Purchase #5	$169.63	5.835%	$179.5279	$179.53	$179.55	$179.50
Purchase #6	$95.39	5.672%	$100.8005	$100.80	$100.80	$100.80
Purchase #7	$248.50	10.562%	$274.7466	$274.75	$274.75	$274.70
7 purchase totals =	$1,024.41		$1,091.8140	$1,091.83	$1,091.90	$1,091.70