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	$134.71	4.244%	$140.4271	$140.43	$140.45	$140.40
Purchase #2	$179.37	5.148%	$188.604	$188.60	$188.60	$188.60
Purchase #3	$137.81	4.156%	$143.5374	$143.54	$143.55	$143.50
Purchase #4	$117.68	4.841%	$123.3769	$123.38	$123.40	$123.40
Purchase #5	$151.61	11.537%	$169.1012	$169.10	$169.10	$169.10
Purchase #6	$46.33	12.643%	$52.1875	$52.19	$52.20	$52.20
Purchase #7	$243.30	11.577%	$271.4668	$271.47	$271.45	$271.50
7 purchase totals =	$1,010.81		$1,088.7009	$1,088.71	$1,088.75	$1,088.70