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	$191.82	3.228%	$198.0119	$198.01	$198.00	$198.00
Purchase #2	$127.78	7.742%	$137.6727	$137.67	$137.65	$137.70
Purchase #3	$92.94	13.702%	$105.6746	$105.67	$105.65	$105.70
Purchase #4	$43.75	4.451%	$45.6973	$45.70	$45.70	$45.70
Purchase #5	$73.47	7.332%	$78.8568	$78.86	$78.85	$78.90
Purchase #6	$87.30	3.502%	$90.3572	$90.36	$90.35	$90.40
Purchase #7	$182.70	9.656%	$200.3415	$200.34	$200.35	$200.30
7 purchase totals =	$799.76		$856.6120	$856.61	$856.55	$856.70