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	$37.55	8.436%	$40.7177	$40.72	$40.70	$40.70
Purchase #2	$101.75	9.390%	$111.3043	$111.30	$111.30	$111.30
Purchase #3	$155.86	8.527%	$169.1502	$169.15	$169.15	$169.20
Purchase #4	$127.77	11.569%	$142.5517	$142.55	$142.55	$142.60
Purchase #5	$244.48	6.192%	$259.6182	$259.62	$259.60	$259.60
Purchase #6	$61.31	4.787%	$64.2449	$64.24	$64.25	$64.20
Purchase #7	$116.69	12.359%	$131.1117	$131.11	$131.10	$131.10
7 purchase totals =	$845.41		$918.6987	$918.69	$918.65	$918.70