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	$123.59	13.196%	$139.8989	$139.90	$139.90	$139.90
Purchase #2	$166.59	7.700%	$179.4174	$179.42	$179.40	$179.40
Purchase #3	$52.27	3.328%	$54.0095	$54.01	$54.00	$54.00
Purchase #4	$144.93	12.411%	$162.9173	$162.92	$162.90	$162.90
Purchase #5	$164.61	13.729%	$187.2093	$187.21	$187.20	$187.20
Purchase #6	$212.88	5.409%	$224.3947	$224.39	$224.40	$224.40
Purchase #7	$111.47	10.223%	$122.8656	$122.87	$122.85	$122.90
7 purchase totals =	$976.34		$1,070.7127	$1,070.72	$1,070.65	$1,070.70