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	$85.72	4.497%	$89.5748	$89.57	$89.55	$89.60
Purchase #2	$121.36	8.595%	$131.7909	$131.79	$131.80	$131.80
Purchase #3	$156.26	7.285%	$167.6435	$167.64	$167.65	$167.60
Purchase #4	$169.42	12.644%	$190.8415	$190.84	$190.85	$190.80
Purchase #5	$103.39	7.807%	$111.4617	$111.46	$111.45	$111.50
Purchase #6	$18.68	6.192%	$19.8367	$19.84	$19.85	$19.80
Purchase #7	$122.60	12.526%	$137.9569	$137.96	$137.95	$138.00
7 purchase totals =	$777.43		$849.1060	$849.10	$849.10	$849.10