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	$148.61	10.696%	$164.5053	$164.51	$164.50	$164.50
Purchase #2	$45.50	6.383%	$48.4043	$48.40	$48.40	$48.40
Purchase #3	$118.60	10.830%	$131.4444	$131.44	$131.45	$131.40
Purchase #4	$139.97	7.476%	$150.4342	$150.43	$150.45	$150.40
Purchase #5	$168.28	3.163%	$173.6027	$173.60	$173.60	$173.60
Purchase #6	$42.57	12.762%	$48.0028	$48.00	$48.00	$48.00
Purchase #7	$133.25	6.250%	$141.5781	$141.58	$141.60	$141.60
7 purchase totals =	$796.78		$857.9718	$857.96	$858.00	$857.90