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	$226.52	13.280%	$256.6019	$256.60	$256.60	$256.60
Purchase #2	$29.25	6.415%	$31.1264	$31.13	$31.15	$31.10
Purchase #3	$235.69	6.157%	$250.2014	$250.20	$250.20	$250.20
Purchase #4	$99.41	7.713%	$107.0775	$107.08	$107.10	$107.10
Purchase #5	$224.79	11.120%	$249.7866	$249.79	$249.80	$249.80
Purchase #6	$166.77	7.678%	$179.5746	$179.57	$179.55	$179.60
Purchase #7	$35.33	8.834%	$38.4511	$38.45	$38.45	$38.50
7 purchase totals =	$1,017.76		$1,112.8195	$1,112.82	$1,112.85	$1,112.90