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	$29.98	6.109%	$31.8115	$31.81	$31.80	$31.80
Purchase #2	$190.54	5.809%	$201.6085	$201.61	$201.60	$201.60
Purchase #3	$61.97	6.325%	$65.8896	$65.89	$65.90	$65.90
Purchase #4	$59.54	12.417%	$66.9331	$66.93	$66.95	$66.90
Purchase #5	$17.96	10.683%	$19.8787	$19.88	$19.90	$19.90
Purchase #6	$196.48	6.564%	$209.3769	$209.38	$209.40	$209.40
Purchase #7	$156.75	11.338%	$174.5223	$174.52	$174.50	$174.50
7 purchase totals =	$713.22		$770.0206	$770.02	$770.05	$770.00