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	$236.84	12.227%	$265.7984	$265.80	$265.80	$265.80
Purchase #2	$183.84	3.516%	$190.3038	$190.30	$190.30	$190.30
Purchase #3	$132.60	12.597%	$149.3036	$149.30	$149.30	$149.30
Purchase #4	$98.57	7.254%	$105.7203	$105.72	$105.70	$105.70
Purchase #5	$38.85	12.314%	$43.634	$43.63	$43.65	$43.60
Purchase #6	$147.80	4.584%	$154.5752	$154.58	$154.60	$154.60
Purchase #7	$162.32	11.831%	$181.5241	$181.52	$181.50	$181.50
7 purchase totals =	$1,000.82		$1,090.8594	$1,090.85	$1,090.85	$1,090.80