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	$246.47	6.298%	$261.9927	$261.99	$262.00	$262.00
Purchase #2	$134.42	4.357%	$140.2767	$140.28	$140.30	$140.30
Purchase #3	$68.54	11.644%	$76.5208	$76.52	$76.50	$76.50
Purchase #4	$38.59	13.831%	$43.9274	$43.93	$43.95	$43.90
Purchase #5	$57.61	6.674%	$61.4549	$61.45	$61.45	$61.50
Purchase #6	$43.89	5.641%	$46.3658	$46.37	$46.35	$46.40
Purchase #7	$45.55	7.302%	$48.8761	$48.88	$48.90	$48.90
7 purchase totals =	$635.07		$679.4144	$679.42	$679.45	$679.50