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	$116.78	12.391%	$131.2502	$131.25	$131.25	$131.30
Purchase #2	$182.37	3.850%	$189.3912	$189.39	$189.40	$189.40
Purchase #3	$66.52	5.787%	$70.3695	$70.37	$70.35	$70.40
Purchase #4	$153.62	9.720%	$168.5519	$168.55	$168.55	$168.60
Purchase #5	$116.29	12.561%	$130.8972	$130.90	$130.90	$130.90
Purchase #6	$101.31	10.600%	$112.0489	$112.05	$112.05	$112.00
Purchase #7	$38.86	9.655%	$42.6119	$42.61	$42.60	$42.60
7 purchase totals =	$775.75		$845.1208	$845.12	$845.10	$845.20