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	$11.70	11.629%	$13.0606	$13.06	$13.05	$13.10
Purchase #2	$89.57	12.429%	$100.7027	$100.70	$100.70	$100.70
Purchase #3	$93.82	8.628%	$101.9148	$101.91	$101.90	$101.90
Purchase #4	$183.28	9.452%	$200.6036	$200.60	$200.60	$200.60
Purchase #5	$238.99	8.331%	$258.9003	$258.90	$258.90	$258.90
Purchase #6	$241.54	9.577%	$264.6723	$264.67	$264.65	$264.70
Purchase #7	$239.89	12.789%	$270.5695	$270.57	$270.55	$270.60
7 purchase totals =	$1,098.79		$1,210.4238	$1,210.41	$1,210.35	$1,210.50