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	$107.35	9.300%	$117.3336	$117.33	$117.35	$117.30
Purchase #2	$40.89	13.680%	$46.4838	$46.48	$46.50	$46.50
Purchase #3	$64.70	10.657%	$71.5951	$71.60	$71.60	$71.60
Purchase #4	$80.84	12.667%	$91.08	$91.08	$91.10	$91.10
Purchase #5	$108.55	7.360%	$116.5393	$116.54	$116.55	$116.50
Purchase #6	$24.85	12.731%	$28.0137	$28.01	$28.00	$28.00
Purchase #7	$176.35	3.702%	$182.8785	$182.88	$182.90	$182.90
7 purchase totals =	$603.53		$653.9240	$653.92	$654.00	$653.90