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	$19.96	9.704%	$21.8969	$21.90	$21.90	$21.90
Purchase #2	$9.62	12.696%	$10.8414	$10.84	$10.85	$10.80
Purchase #3	$42.45	3.808%	$44.0665	$44.07	$44.05	$44.10
Purchase #4	$83.97	6.786%	$89.6682	$89.67	$89.65	$89.70
Purchase #5	$69.98	12.179%	$78.5029	$78.50	$78.50	$78.50
Purchase #6	$171.99	3.826%	$178.5703	$178.57	$178.55	$178.60
Purchase #7	$38.35	6.188%	$40.7231	$40.72	$40.70	$40.70
7 purchase totals =	$436.32		$464.2693	$464.27	$464.20	$464.30