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	$122.49	13.586%	$139.1315	$139.13	$139.15	$139.10
Purchase #2	$31.68	5.616%	$33.4591	$33.46	$33.45	$33.50
Purchase #3	$164.67	10.763%	$182.3934	$182.39	$182.40	$182.40
Purchase #4	$105.25	3.647%	$109.0885	$109.09	$109.10	$109.10
Purchase #5	$21.47	13.713%	$24.4142	$24.41	$24.40	$24.40
Purchase #6	$90.36	5.451%	$95.2855	$95.29	$95.30	$95.30
Purchase #7	$124.87	5.122%	$131.2658	$131.27	$131.25	$131.30
7 purchase totals =	$660.79		$715.0380	$715.04	$715.05	$715.10