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	$240.38	3.440%	$248.6491	$248.65	$248.65	$248.60
Purchase #2	$196.89	10.371%	$217.3095	$217.31	$217.30	$217.30
Purchase #3	$47.62	13.856%	$54.2182	$54.22	$54.20	$54.20
Purchase #4	$157.60	4.555%	$164.7787	$164.78	$164.80	$164.80
Purchase #5	$235.69	11.680%	$263.2186	$263.22	$263.20	$263.20
Purchase #6	$83.59	10.699%	$92.5333	$92.53	$92.55	$92.50
Purchase #7	$30.65	3.140%	$31.6124	$31.61	$31.60	$31.60
7 purchase totals =	$992.42		$1,072.3198	$1,072.32	$1,072.30	$1,072.20