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	$60.27	12.569%	$67.8453	$67.85	$67.85	$67.80
Purchase #2	$177.88	11.589%	$198.4945	$198.49	$198.50	$198.50
Purchase #3	$100.90	8.298%	$109.2727	$109.27	$109.25	$109.30
Purchase #4	$110.48	5.743%	$116.8249	$116.82	$116.80	$116.80
Purchase #5	$137.61	7.189%	$147.5028	$147.50	$147.50	$147.50
Purchase #6	$168.56	8.256%	$182.4763	$182.48	$182.50	$182.50
Purchase #7	$66.27	4.187%	$69.0447	$69.04	$69.05	$69.00
7 purchase totals =	$821.97		$891.4612	$891.45	$891.45	$891.40