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	$105.82	10.663%	$117.1036	$117.10	$117.10	$117.10
Purchase #2	$136.53	12.264%	$153.274	$153.27	$153.25	$153.30
Purchase #3	$168.81	5.569%	$178.211	$178.21	$178.20	$178.20
Purchase #4	$133.88	11.589%	$149.3954	$149.40	$149.40	$149.40
Purchase #5	$74.81	10.403%	$82.5925	$82.59	$82.60	$82.60
Purchase #6	$167.99	11.254%	$186.8956	$186.90	$186.90	$186.90
Purchase #7	$82.56	10.138%	$90.9299	$90.93	$90.95	$90.90
7 purchase totals =	$870.40		$958.4020	$958.40	$958.40	$958.40