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	$81.29	5.227%	$85.539	$85.54	$85.55	$85.50
Purchase #2	$168.31	10.407%	$185.826	$185.83	$185.85	$185.80
Purchase #3	$243.44	6.579%	$259.4559	$259.46	$259.45	$259.50
Purchase #4	$76.55	5.267%	$80.5819	$80.58	$80.60	$80.60
Purchase #5	$220.36	11.462%	$245.6177	$245.62	$245.60	$245.60
Purchase #6	$40.75	7.257%	$43.7072	$43.71	$43.70	$43.70
Purchase #7	$60.26	9.446%	$65.9522	$65.95	$65.95	$66.00
7 purchase totals =	$890.96		$966.6799	$966.69	$966.70	$966.70